Hercule Poirot has fallen out of favour with Scotland Yard. When he receives letters threatening murder and no one is willing to listen, the once great detective must take matters into his own hands.

The A.B.C. killer sends Hercule more ominous letters promising to spill blood. Hercule's past, integrity, authority and identity all come into question while he fights the atmosphere of rising xenophobia in Britain.

Without any warning, the A.B.C. murderer strikes again. Hercule and Crome arrive at the crime scene, once again too late.

As the A.B.C. killer is on the loose, Hercule realises that only he holds the key to the murders. He faces a race against time to stop the bloodbath.