| Cast overview, first billed only: |
 | Zdenek Stepánek | - | Man from the unknown / John Graigs - american industrialist |
 | Jirina Stepnicková | - | Helena - Craigs's wife |
 | Zvonimir Rogoz | - | Clifford - Craigs's secretary |
 | Karel Cerný | - | Black - director of steel mill |
 | Karel Dostal | - | Vice-president Northon |
| Jaroslav Prucha | - | MUDr. White - doctor |
| Bozena Sustrová | - | Nelly Werner - Craigs's mistress |
 | Frantisek Kreuzmann | - | Bob |
| Jarmila Holmová | - | Bob's wife |
 | Vladimír Smeral | - | Dvorácek - patient |
 | Jaroslav Vojta | - | Laborer in steel mills |
 | Marie Buresová | - | Girl from the port |
| Bolek Prchal | - | Police Commissioner |
 | Vladimír Hlavatý | - | Reporter |
| Rudolf Hrusínský | - | Editor |
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