In Puerto Rico to investigate a glut of contraband diamonds that are flooding the world's jewel market, Mr. Moto and his sidekick, a wrestler, find themselves involved in murders by thrown daggers, the frame-up of an overstressed Army colonel, and a pirate gang led by an unknown boss who has inside knowledge of the ensuing investigation.
| Directing | Herbert I. Leeds | Director |
| Writing | John W. Vandercook | Novel |
| Writing | John P. Marquand | Characters |
| Writing | George Bricker | Story |
| Writing | John Reinhardt | Story |
| Writing | Peter Milne | Screenplay |
| Production | John Stone | Producer |
| Directing | William Forsyth | Assistant Director |
