Agatha Christie's The ABC Murders features Hercule Poirot hunting a serial killer who follows an alphabetical pattern in their victim selection. While a salesman named Cust is the primary suspect, Poirot uncovers that the letters are a decoy for a specific, premeditated murder. You can legally borrow this classic mystery as an eBook or audiobook through services like Libby and Hoopla. The ABC Murders by Agatha Christie