"The Plymouth Express Affair" is indeed a short story written by Agatha Christie, featuring her famous detective Hercule Poirot. It was first published in the collection "Murder in the Calais Coach" in the United States and later in the UK under the title "Murder on the Orient Express." In "The Plymouth Express Affair," Poirot investigates the murder of a wealthy American heiress named Ruth Kettering, who is found dead aboard the Plymouth Express train. The circumstances surrounding Ruth's death are mysterious, and there are several suspects with plausible motives. As Poirot delves into the case, he uncovers a tangled web of secrets, lies, and betrayals among Ruth's family and acquaintances. With his astute observation and deductive reasoning, Poirot sifts through the clues and interrogates the suspects to uncover the truth behind Ruth's murder. "The Plymouth Express Affair" is a classic example of Agatha Christie's mastery of the detective genre, featuring a meticulously plotted mystery, a cast of intriguing characters, and a surprising twist at the end. It showcases Christie's ability to keep readers guessing until the very end and her talent for creating memorable and suspenseful whodunits.