The ABC Murders

In 1933, an older Hercule Poirot receives a series of letters from someone who signs themself only as A.B.C. Each message hints at another murder, but the police find little they can do with the warnings, while Poirot discovers that the people he once relied on have moved on. When a killing finally takes place, the retired detective begins pursuing the sender himself and is drawn into a case involving victims chosen according to an alphabetical pattern.