Billionaire playboy Oliver Queen, missing and presumed dead after a shipwreck that claimed the life of his father, Robert, is discovered alive after five years on a remote Pacific island. He is welcomed home to Starling City by his mother Moira, stepfather Walter Steele, younger sister Thea, and best friend Tommy Merlyn, but they sense he has changed. Moira assigns John Diggle as Oliver's bodyguard. Oliver hides the truth about the man he has become, and tries to reconcile with his former girlfriend, Laurel, whom he cheated on with her sister Sara (who died in the shipwreck). While reconnecting with those closest to him, by night Oliver secretly masquerades as a hooded vigilante archer, attempting to fulfill his dying father's entreaty: to right the wrongs of his family. Oliver's first goal is to take down corrupt millionaire Adam Hunt, who has scammed millions from various people in the city. Laurel's father, police detective Quentin Lance, becomes determined to arrest the vigilante. Meanwhile, it is revealed Oliver's mother has an agenda at odds with her son, having orchestrated a kidnapping to determine what Robert told him after the shipwreck.
Laurel brings a civil suit against millionaire Martin Somers, who is also one of Oliver's targets, for taking part in drug trades with the Triad that ultimately led to the death of a young woman's father. As the vigilante, Oliver threatens Somers to make him confess to the murder as penance for all of the wrongs he has done to the city. Instead, Somers contacts the Triad, who send the assassin Chien Na Wei to kill Laurel. Oliver saves Laurel from Chien; he later obtains Somers' confession and gives an audio recording of it to Quentin. Meanwhile, Moira and Walter push Oliver to take a position at the company. Oliver stymies their efforts by using the opening of the company's new applied sciences division to publicly opt out of the position, knowing that he cannot simultaneously honor Robert's request to fight for the city and be the man Moira wants him to be. She is revealed to be conspiring with a man affiliated with a symbol that exists in Robert's book possessed by Oliver. A flashback to Oliver's time on the island shows him being attacked by an unknown hooded figure wielding a bow and arrow.
Oliver tracks down another millionaire from his list, before the latter is killed by an assassin known as Deadshot. Oliver decides to build a new dance club above his hideout as a cover for his nighttime disappearances. While comparing the competition, he finds Thea, who reveals that Laurel and Merlyn had been involved during Oliver's absence. Laurel becomes suspicious when Oliver does not react to it, and concludes he already knew. She and Merlyn start dating again. Meanwhile, Oliver uses the assassin's M.O. to learn his true identity, Floyd Lawton, and his assignment to kill businessmen including Walter at an auction. As the vigilante, he enlists the help of Quentin to prevent Lawton's plan. Oliver succeeds, apparently killing Lawton in the process, but Diggle is shot during the fight. In order to save Diggle's life, Oliver is forced to reveal his dual identity to him. Flashbacks reveal that the Asian archer who attacked Oliver was actually trying to help him; Oliver misunderstands and escapes; and is revealed to be pursued by an unknown group of armed men.
Oliver offers Diggle a chance to fight at his side and help the city, which the latter refuses. Later, Oliver discovers a connection between Peter Declan, a death row inmate, and Jason Brodeur, one of the men on his list. As the vigilante, he enlists the help of Laurel to prove Declan's innocence. Working together, the pair uncovers the truth, but Brodeur has his mercenaries stage a prison riot so that they can have Laurel and Declan killed before the truth is revealed. Oliver sneaks into the prison dressed as a guard and saves the two, with her realizing that the vigilante is merciless. Declan is exonerated while Brodeur is arrested. Diggle meets with Oliver and agrees to work with him so that he can both protect the city and protect Oliver from losing his humanity. Quentin arrests Oliver on suspicion of being the vigilante. Meanwhile, Walter discovers that Moira has been keeping the salvaged and sabotaged family yacht hidden in a warehouse. Flashbacks show that the archer forced Oliver to kill a bird for food, making it the latter's first kill. He was also taught to forget Laurel.
Oliver hires Laurel as his attorney and his bail is accepted. Given Oliver's time on the island, the District Attorney offers an insanity plea with indefinite treatment for post-traumatic stress disorder in a psychiatric facility. Oliver declines, instead offering to take a polygraph test to prove his innocence, which he passes. While remanded under house arrest, Oliver throws a prison-themed party, maintaining his bachelor playboy facade. He has Diggle pose as the vigilante and stop a German arms dealer who is in the city to sell automatic weapons to the city's gangs. The plan works and the charges are dropped after Quentin kills a man who was sent by Moira's co-conspirator to kill Oliver. However, Laurel begins to suspect Oliver. Moira threatens her associate to stay away from her family. Walter leaves the house after confronting Moira on her lies. Flashbacks show Oliver caught and tortured by the armed men, led by Edward Fyers, for the location of the archer, who is revealed to be a former military officer, before being saved by the latter.
Oliver begins preparing to attack another individual from the list, but Diggle argues that he should expand his work and help the police stop a group of bank robbers. Oliver initially refuses, believing that it detracts from his mission to right Robert's wrongs, but agrees finally. The former deduces that the robbers are actually a family unit, and that the leader Derek Reston worked for Queen Industries before Robert outsourced 1500 jobs to China and the Reston family lost their home as a result. Feeling guilty, Oliver tries to persuade Derek to right his own wrongs, but learns that the family are going to rob another bank. During Oliver's confrontation, Derek is fatally shot. Meanwhile, Merlyn throws Laurel a fundraiser to support her law firm, CNRI, hoping to prove his love for her that way. Oliver and Moira manage to regain their emotional connection. Flashbacks show Oliver having a dream of Robert blaming him for his idleness and reveal how Oliver first discovered the target names in his father's notebook.
Moira is almost shot by a mysterious assailant who was attempting to assassinate an associate of mob boss Frank Bertinelli. Oliver attempts to infiltrate Frank's business to discover the identity of the attacker. Frank blames Chien and the Triad gang for the murders of his people. Oliver learns that the attacker is Helena Bertinelli, Frank's daughter, with whom the former had just been on a date. Helena reveals that she is looking for revenge against her father, who she blames for the murder of her fiancé, who according to Frank was gathering evidence against him to give FBI. Helena and Oliver are abducted by Frank's right-hand man, Nick Salvati, in connection to the deaths; she reveals that she was the one gathering evidence and kills Salvati after learning he was the one who killed her fiancé. She also deduces Oliver's identity as the vigilante after witnessing him fight Frank's henchmen. In the end, Helena and Oliver share a kiss. Meanwhile, Tommy is cut off financially by his father, Malcolm, who is revealed to be Moira's co-conspirator. Laurel sticks with him, stating that she does not want him for money. Walter returns home.
Oliver decides to teach Helena that there is justice outside of revenge after witnessing her try to kill the head of the Triad. Diggle expresses his disapproval, but to no avail. She dresses as a purple vigilante and the duo has another man from the list arrested. Helena starts to buy into the idea, but leaves him after finding out that Laurel was his former girlfriend and believing that they are still together. Helena goes after the Triad, killing their leader. As a result, Chien and her men go after Frank, believing him to be responsible, but Oliver gets there in time to stop them. Oliver also stops Helena from killing Frank, who is arrested; and she threatens to reveal his identity if he tries to come after her in the future. Meanwhile, Tommy finally tells Oliver about Malcolm's action and asks for a job at the club that Oliver is attempting to build, which is accepted. Using Felicity's help, Walter learns more about the secret organization that Moira is a part of, finding a notebook containing the list.
Hunt is killed by a mysterious archer. Quentin deduces that a copycat is at work, but his superior publicly blames the hooded vigilante. Oliver plans a Christmas party at the mansion to bring back the spirit of the holidays to his family. He saves some hostages from the archer, and the two archers are injured after fighting, with Oliver realizing that Robert wasn't the author of the list. The archer escapes and is revealed to be Malcolm. Walter finds out about the vigilante's objective and is kidnapped by one of Malcolm's associates. The organization's plan is revealed to be starting six months later, when thousands of people will die for what it believes to be for the greater good. Flashbacks show the Chinese archer, Yao Fei, capturing Fyers, who tells Oliver that the island was a prison for dangerous criminals and that his unit was tasked to exterminate the inmates, including Yao, after the program was shut down. Yao is captured by the unit while leading Oliver to a possible escape from the island; and the latter escapes.
Six weeks after his fight with Malcolm, Oliver avoids any activities as his vigilante, despite insistence from Diggle. When a firefighter is killed in the line of duty, Laurel suspects that he was murdered and steals the phone the vigilante gave Quentin in order to contact him for help. Tracking down the suspect, Oliver is overpowered during the confrontation, but discovers that the murderer is a former firefighter. Oliver learns that the murderer is Garfield Lynns, a firefighter thought to have died in a massive fire several years prior, but survived with severe burns. Lynns shows up at a fundraiser held for support of the victims in order to kill the fire chief. As the vigilante, Oliver saves the chief before Lynns commits suicide. The media calls the vigilante a hero while Oliver decides to continue his hunt of the list members. Moira decides to take over for Walter as C.E.O. Quentin plants a listening device on the phone to monitor Laurel's communications with the vigilante. Flashbacks show Oliver killing a mercenary, wearing his uniform and recovering his tools, including a map.
After an armored truck is robbed, Oliver believes that one of the thieves is former Marine Ted Gaynor, from his target list. Diggle dismisses Oliver's assumption, as Gaynor was Diggle's commanding officer during his time in Afghanistan. Oliver finds Gaynor and steals encrypted data, as Diggle prevents the former from getting any information directly from Gaynor. The data is revealed to be plans for robbing armored trucks, which Oliver uses to track the thieves. Diggle learns that Gaynor was the mastermind behind the robberies, and is forced to join Gaynor's team, but backs out of helping them at last. Oliver arrives in time and kills Gaynor. Meanwhile, Thea tells Oliver her belief that Moira and Malcolm are involved as the former believes they were before Robert's death. Oliver asks Moira, who states Robert was the unfaithful. Tommy refuses Malcolm's request to sign the paper of selling the clinic established by the former's mother, who died when he was 8 and Malcolm left him for years subsequently. Thea is arrested by the police after having a crash as a result of drug use. Flashbacks show Oliver being captured by the mercenaries as Yao was apparently working for them.
The judge dismisses the plea bargain of Thea and orders the charges brought to trial. Helping Thea, Oliver begins working on tracking down the supplier of the drug, which is known as Vertigo; he discovers that the supplier is called "The Count", and arranges a meeting through his contacts with the Russian mob. The meeting is broken up by the police, and the Count injects Oliver with a dose of Vertigo. While showing the effects of overdose, the latter still continues his investigation. He uses the ingredients to track the location of the Count. As the vigilante, Oliver is able to confront the Count and inject him with Vertigo, causing irreparable damage. Laurel persuades Quentin to get Thea community service and two years of probation, which she begins serving at Laurel's legal office. Felicity shows Oliver the list of names that Steele discovered, and informs him that they came from Moira. Flashbacks show Yao overpowering Oliver in a mandatory duel and making him appear dead. His body is thrown to a waterfall, where he wakes up and finds an upgraded map, planted by Yao.
Moira denies knowledge about the list. Diggle decides to investigate her daily activities. Laurel enlists the help of the vigilante when criminal Cyrus Vanch is released from prison. Using the microphone inside the phone, Quentin and his team intercept the vigilante, who manages to escape. Vanch kidnaps Laurel. Quentin and the vigilante team up to save Laurel, as the former realizes that Vanch has contacts on the police force and that was how he learned of her. The duo saves Laurel. She demands Quentin to stay away from her for betraying her trust. In order to protect her, Oliver decides to cut his contact with her as the vigilante. Diggle presents evidence to Oliver that his mother is connected to the group he is hunting, and that she also knew of Robert's yacht. Oliver decides to interrogate his mother as the vigilante. In flashbacks, Oliver meets Slade Wilson, an Australian Intelligence operative who came to the island to free Yao Fei. It is revealed that the masked mercenary who tortured Oliver was Wilson's partner; and Wilson has the same mask. He starts training Oliver to get him ready to infiltrate the airfield, the only apparent way out.
Oliver is critically shot by Moira and escapes. He exposes his secret to Felicity, and asks her to take him to his hideout. With Diggle's help, the bullet is removed and Oliver is stabilized. Felicity refuses to join Oliver's fight, but decides to help them find Steele. Oliver convinces Diggle to stop investigating Moira until they find out more about the organization. Flashbacks show Oliver being trained. Wilson reveals that his former partner is Billy Wintergreen, who was sent with Wilson to find out Fyers' mission. Their plane was shot down and they were captured by Fyers' men. Wintergreen accepted Fyers' offer to change sides. After infiltrating the airstrip, Wilson reveals plans to send in an airstrike to wipe out all of Fyers' operation. Oliver heads out to save Yao, but is recaptured by Fyers. Before he can be executed, Wilson arrives, rescuing Oliver and killing Wintergreen. Although they miss the supply aircraft, Wilson and Oliver decide to continue to work together to get off the island, with the former stating that Fyers is hired by another party for a purpose. Yao is revealed to have changed sides because his daughter, Shado, is held captive by Fyers.
Oliver learns of a jewel thief named "Dodger", who uses hostages tagged with bomb collars. Felicity suggests that Oliver bug the phone of Detective McKenna Hall, an old friend of Oliver's, to gain information on the Dodger. She also convinces Oliver to ask Hall out on a date so that he can have some down time. Through the wire tap, Oliver is able to determine the Dodger's next location, but is stunned by a bomb thrown by the thief, who gets away. To draw out the Dodger, Oliver donates antique jewels to an auction. It works; but when Felicity confronts the thief, he places a collar on her to ensure his getaway. Oliver manages to stop the Dodger and deactivate the collar. Diggle starts dating his former sister-in-law. Thea has a run-in with a thief named Roy Harper, and Moira attempts to make a deal with Chien to have Malcolm killed, so that she can leave the secret organization, whose plan is called the "Undertaking". Flashbacks show Oliver trying to treat Wilson's infected wound by finding the herbs Yao used; and is intercepted by a wounded man who asks for help; but Oliver leaves him as the former believes it to be a trap.
Oliver kills a hired gunman, and realizes that the latter's target is not safe yet. Chien hires Lawton, who is revealed to have survived Oliver's attack, to take out Malcolm after the previous gunman's death. Malcolm asks Tommy to attend an award ceremony where Malcolm will be receiving a humanitarian award; Tommy is persuaded by Oliver to attend. At the last moment, Oliver discovers that Malcolm is the target and races to the event to save him. Although he is almost caught by Hall, Oliver manages to get Malcolm away from Chien's men. Malcolm is shot with one of Lawton's poisonous bullets, and Oliver is forced to reveal his identity to Tommy so that he can save Malcolm's life. Malcolm and Tommy reconcile. The former tells Moira about his belief that someone from the organization attempted to kill him. Laurel is confronted by her mother, Dinah, who states that Sara, the former's sister, might be alive. During a flashback, Oliver is shown repairing a damaged radio, which Wilson uses to tune into the radio communications of Fyers. They find out that Fyers possesses an advanced anti-aircraft missile launcher.
Helena returns to Starling City to kill Frank after she learns that he plans to make a deal with the F.B.I. for witness protection. Oliver opens his nightclub and refuses her request for help; and she attacks Tommy to force his assistance. Helena is captured by the police's trap. Oliver breaks her out to protect his secret and demands that she leave Starling City. Instead, she forces Felicity to find Frank's location. Oliver manages to stop Helena from killing Frank;, but when Hall arrives, Helena shoots her and escapes. In the hospital, Hall breaks up with Oliver, heading to Helena's tarnish on Oliver's character. Meanwhile, Tommy's knowledge of Oliver's secret affects his relationship with Laurel; but the former reconciles with Oliver. Dinah presents her evidence of Sara's existence to Quentin and Laurel. Thea and Roy get closer. In a flashback to the island, Oliver and Wilson steal the circuit board of the anti-aircraft missile launcher, which the latter states can start a war, and offer Fyers a trade of the board with a way out of the island.
Another vigilante appears in Starling City and kidnaps one of Oliver's targets, a slumlord who had charges dropped against him because he was able to pay off the District Attorney. The new vigilante, who is identified as Joseph Falk, kills the slumlord over a live broadcast. The former kills several prosecutors the same way before going after Harper. Diggle finds out that Falk is using an abandoned subway car, and Oliver is able to catch the car and kill Falk. Oliver realizes the secret organization's plans involve The Glades, a neighborhood filled with crime. Laurel proves to Dinah and Quentin that Sara is not alive. It is revealed that Dinah knew of Sara's plan to escape with Oliver. Malcolm contacts the Triad to find the traitors. Moira turns over her co-conspirator, Frank Chen, to Malcolm, who kills Chen, believing her to be innocent. Flashbacks to the island show Oliver and Wilson freeing Shado, but at the cost of Fyers reacquiring the board. She claims to know Fyers' scheme.
When a girl dies after using a new form of Vertigo, Oliver sets out to interrogate the Count and determines the latter has lost his mind from the Vertigo overdose. When news reports state that the Count escaped the asylum, Oliver suspects that the Count was faking his mental illness. Meanwhile, Quentin finds loose connections between Tommy and Vertigo, and attempts to uncover the truth, which almost leads him to discovering Oliver's hideout. Oliver realizes that the Count's psychiatrist is behind the re-emergence of Vertigo. Oliver kills the doctor, and opts not to kill the Count, who has truly lost his mind and was the scapegoat of the doctor's actions. Tommy quits the club after realizing that Oliver suspected him with the drug dealing. Malcolm gives him a job. Oliver decides to help Diggle find Lawton, who killed Diggle's brother. In a flashback, Shado reveals that Yao Fei took the blame of a massacre committed by the Chinese government and was exiled to the island. Now Fyers is using him as a scapegoat for his schemes. She begins training Oliver to use a bow.
Laurel represents the Moore family who are suing a corrupt businessman, who puts a hit on the family, and the couple's young child is the sole survivor. Laurel takes the boy into her custody and is saved by the vigilante from the hitman's attempt. Tommy suggests that they go to Oliver's for protection. An operation headed up by A.R.G.U.S, a government organization, is set to capture Lawton, but Oliver chooses the Moores case. As a result, Lawton escapes and Diggle decides to leave Oliver, who forces the businessman to confess his crimes, leading to the latter's arrest. After killing the latter, the hitman comes to the Queen residence to kill all remaining witnesses, but Oliver manages to kill him. Tommy decides to leave Laurel, believing that he could never compete with Oliver should she discover that he is the vigilante. Elsewhere, Roy starts searching for the vigilante; and Thea agrees to help. During a flashback to the island, Shado continues teaching Oliver to use a bow before Yao Fei brings Fyers' men to their hideout.
Oliver tracks down an accountant of the secret organization and steals his laptop. While decrypting it, Felicity uncovers a link to Walter—a money transfer was made to Dominic Alonzo, an underground casino owner who was hired to kidnap Walter. The pair infiltrate the casino; and Alonzo claims that Walter was killed. Oliver informs his family and Moira confronts Malcolm, who proves to her that Walter is still alive. Oliver, who was listening in, discovers that Malcolm is heading the secret organization, and uses Felicity to ascertain Walter's location. As the vigilante, Oliver frees Walter. Meanwhile, Laurel asks Tommy for the truth about why he left, and Tommy states that Oliver still loves her, a claim he confirms. He asks Diggle to help him stop the "Undertaking". In a flashback, Robert is shown disagreeing with Malcolm's proposed "Undertaking", which would involve leveling the Glades with a machine, which will be built in five years, and killing thousands of people in order to rebuild the area. As a result, Malcolm has a bomb planted on the Queens' yacht just before Robert boards it to head to China for his plan to stop the former.
Malcolm kills the scientists who worked on the device. Diggle dresses as the vigilante and kidnaps Oliver and Moira in an attempt to uncover the truth. The plan works and Oliver's team breaks into Malcolm's company for information. Quentin finally approves Laurel's feelings for Oliver, who realizes that he could cease being the vigilante if he stops the Undertaking. Thus, Oliver gets involved with her again, which is seen by Tommy. Malcolm has the device moved. The vigilante attempts to kill him, who reveals that he is the other archer; the two fight until Malcolm gets the upper hand, discovering Oliver's secret. Meanwhile, Walter files for divorce, revealing to know Moira's involvement in his kidnapping. Roy reveals to Thea that he wants to find the vigilante so that the latter can train the former, pushing her away from himself. In a flashback, the man Oliver chose not to help previously is revealed to be working for Fyers, who reveals that he plans to cripple the Chinese economy by blowing up commercial planes going into the country. His employer is revealed to be a woman. He murders Yao Fei after forcing him to take credit for the attacks via video recording.
Malcolm imprisons Oliver; but the latter manages to escape. He confronts Moira about the Undertaking, which prompts her to hold a press conference and reveal to the city her involvement with Malcolm and the plan to destroy the Glades. She is arrested while Malcolm confirms her claims to Tommy and reveals that he is the other. Quentin, with help from Felicity, is able to dismantle the device. Diggle and Oliver go after and mortally wound Malcolm, who reveals that there is a second device shortly before he dies. The device activates and begins to level the east side of the Glades. Thea goes into the Glades to save Roy, who decides to stay and help others. Laurel is trapped in her office; but Tommy arrives and helps her escape before being trapped himself. Oliver arrives too late, and Tommy dies. In a flashback, Fyers fires a missile at an approaching airliner, but Oliver and Shado manage to override the coordinates and destroy the missile. Afterward, Oliver kills Fyers, revealed to have gained relative skill with bow.