Eight-year-old Roger Court is in Venice expecting to reunite with his father, British diplomat Major Court (Trevor Howard), whom he hasn't seen in three years. Roger lives with his Aunt Rose since his mother abandoned him.
| Actor | Role |
|---|---|
 Richard O'SullivanRoger Court | Roger Court |
 Alida ValliRoberta Gleukovitch | Roberta Gleukovitch |
 Eduardo CiannelliDr. Vivaldi | Dr. Vivaldi |
 Trevor HowardMajor Roger Court | Major Roger Court |
 Richard BasehartJoe Hamstringer | Joe Hamstringer |
 Stephen MurrayBritish Consul in Venice | British Consul in Venice |
 Arnoldo FoàCommissioner | Commissioner |
 Guido CelanoChief Constable | Chief Constable |
 Helen GossUndetermined Role | Undetermined Role |
| GGiorgio CostantiniPescovitch | Pescovitch |
| AAngelo CecchelinLuza | Luza |
| NNino VechinaFirst Killer | First Killer |
| AArmando PapetteSecond Killer | Second Killer |
| GGiovanni KaruzThird Killer | Third Killer |
| JJoan ButterfieldMrs. Harrington | Mrs. Harrington |
| AAlessandro PaulonMorgan | Morgan |
| RRemington OlmstedRamondo | Ramondo |
| JJacopo TecchiNot listed | Not listed |