Celebrated crime writer Colin Knowles finds himself at the centre of a baffling real-life mystery when his estranged wife Louie asks for his help. Her new boss has gone missing at his grand country home -- and when his body is found, the hunt is on for a devious and twisted murderer. Sinister letters from London refer to a 'double crime'. Who will be the killer's next victim?

A man and a woman are poisoned. The woman dies, but the man survives. The finger of blame begins to point at the man. A policeman and a newspaper journalist pursue the truth.