- Milton Conrad (listed as “Hillary Conrad” in Credits) - Antony Eustrel
- Ben Gazzman - Bob Michaels
- Contessa Montenegro - Maureen Arthur
- Omar Shurok - Raoul Franck
- Otto Von Werner - Tol Avery
- Despite repeated references to an "exploding" birthday cake, the cake does not actually explode. Instead, it has a model cannon mounted on it which fires at the victim when he blows out the candles.
- The title refers to the term "whodunit", a sub-genre of detective fiction.