Hercule Poirot's quiet supper in a London coffee house is interrupted when a young woman confides to him that she is about to be murdered. She is terrified, but begs Poirot not to find and punish her killer. Once she is dead, she insists, justice will have been done. Later that night, Poirot learns that three guests at a fashionable London hotel have been murdered, and a cufflink has been placed in each one's mouth. Could there be a connection with the frightened woman? While Poirot struggles to put together the bizarre pieces of the puzzle, the murderer prepares another hotel bedroom for a fourth victim.
