Ballantine Mystery: The Player on the Other Side

More about the book

A card with the letter "J" on it appeared in Robert York's mail, and a day later he was dead. Then another card showed up, and Ellery Queen knew he was up against a brilliant killer who made a game of death by warning his victims. The only clue was the signature "Y" and Ellery had to find him and stop his remorseless vendetta before "Y" won his mad game...