Martin, a graduate student at Oxford, seeks mentor-ship from the renowned Arthur Seldom. Their professional relationship shifts when they discover the body of Martin's landlady. Seldom claims he received a threatening note, suggesting a serial killer is using mathematical logic to taunt him. As subsequent deaths occur, each marked by a geometric symbol, the pair attempts to decode the sequence. Martin becomes romantically involved with Lorna, a nurse who remains deeply connected to the hospital and the social circles surrounding Seldom. As the mystery deepens, Martin realizes the danger is not a single genius playing games, but rather a chaotic collision of human desperation, resentment, and manipulation that leaves the investigators questioning the very nature of truth.