Bates plays the titular Oliver (it is never made clear whether this is his first or last name), a keen word-game enthusiast and lecturer in comparative religion. After his teaching post is made redundant, he resolves to make use of his new wealth of free time by going to visit his favourite crossword compiler, 'Aristotle', with whom he has corresponded but whom he has never met. When he arrives, however, he finds Aristotle's house has been ransacked and its occupant has departed for parts unknown, and he sets out to discover why.
Accompanied by WPC Diane Priest (Cusack) (suspended from the police for voicing suspicions about a senior officer), and doggedly pursued by the mysterious Mr. Baxter (Paterson), he finds himself caught up in all manner of nefarious activities, leading from South Wales to a surprising twist ending in the Orkney islands.
The series was developed from Alan Plater's own novel.