Based on a novel by Cortland Fitzsimmons, the storyline of this "gimmick" mystery follows the St. Louis Cardinals during a championship season. The arrival of hotshot pitcher Larry Kelly (Robert Young) coincides with an apparent plot to sabotage the Cards' chances of making it to the World Series. A failed attempt to poison all the pitcher's mitts is followed by a series of murders: catcher Dunk Spencer (Joe Sauers) is shot while sprinting to third base, pitcher Frank Higgins (Robert Livingston) is strangled in the locker room, and lovable catcher Truck Hogan (Nat Pendleton) is killed with an arsenic-laden hot dog. Finding himself one of the many suspects, Kelly nearly becomes a victim as well when he is slipped a booby-trapped baseball. With the help of sportscaster Jimmy Downey (Paul Kelly), Kelly exposes the murderer, surviving to win the pennant and the heroine, team secretary daughter Frances Clark (Madge Evans). Partly filmed on location at Los Angeles' Wrigley Field (home of the Chicago Cubs' minor-league LA farm team), Death on the Diamond offers a fresh slant to the standard whodunit format, with some particularly good work by Ted Healy as an exasperated umpire. That MGM produced the film is tipped off by two of the studio's trademarks: The killer's last-minute confession, wherein the guilty party transforms from a mild-mannered soul into a raving lunatic, and the shoddy process-screen work in the ballgame scenes. Future stars Mickey Rooney, Walter Brennan and Bruce Bennett show up in bit roles.