On August 11, 2014, SM Entertainment announced Taemin would release an EP entitled Ace on August 18. On August 13, a highlight medley video from the EP was uploaded to YouTube. The official music video for the EP's first single, "Danger", came out on August 15.
The song "Danger" was composed by Thomas Troelsen, who also wrote the theme song for the World Cup in Brazil. On radio show Blue Night Radio a listener asked Taemin, "I liked the shooting sound in your music program performances. Why isn't it included in the digital version [of the song]?" Taemin said, "It was added right before performing on a music program as effect sounds for performance. It's not included because it may damage the musical completion of the song." Another listener asked, "'Danger' has a Michael Jackson feel. Did you have it in mind while working on the song?". To this, Taemin replied,"The song was composed abroad and bought. It wasn't like our goal or role model but just happened so in the process. The company thought it would suit me well, and it's not a style I dislike."
The song's choreography was created by Ian Eastwood. Shinee member Jonghyun also added that he heard from the managers that after seeing Taemin dance, "I heard he found it amazing for you to copy him so well." Eastwood says of the song is "...like Michael Jackson" and pays homage to Jackson's unique dance moves and that Taemin seems to understand what Jackson's performance means.
Korean music publication Weiv described the track "Danger" as "[...] a song that showcases the bright sense of Thomas Troelsen good at using multiple tracks, stands out. Most of all, it is a rare song among recent SM songs which doesn't tire you after many replays." IZE said "the young mysterious thief character with light moves but serious business came to life with Taemin's performance."