The ABC Murders Episode 1.01 Episode 1

1933. Hercule Poirot, older and greyer, receives letters threatening murder. The sender signs themselves only as "A.B.C." When he takes the letters to the police looking for help Hercule finds all his old friends have moved on. But soon there is a murder, and in order to have any hope of catching the killer, the once great detective must take matters into his own hands.