It's 1933, and an older and greyer Hercule Poirot receives letters threatening murder. When no-one listens to his appeals, the once great detective must take matters into his own hands.

The ABC killer sends more letters promising to spill blood. Hercule's past, integrity and identity come into question while he fights a rising tide of xenophobia.

With the ABC killer still on the loose, Hercule realises that only he holds the key to the murders. He faces a race against time to stop the bloodbath.