The Spanish merchant "Mare Nostrum", captained by Ulises Ferragut, docked in September 1939 at the port of Naples to repair a breakdown. Walking through the ruins of Pompeii, Ferragut meets Freyra, an enigmatic and beautiful woman of whom she instantly falls madly in love, unaware that the girl is in fact a dangerous spy of the Third Reich.
| Actor | Role |
|---|---|
 María FélixFreyra | Freyra |
 Fernando ReyUlises / Capitán Ferragut | Ulises / Capitán Ferragut |
 Guillermo MarínVon Kramer / Conde Gavelin | Von Kramer / Conde Gavelin |
 José NietoKurt | Kurt |
 Juan EspantaleónTío Caragón | Tío Caragón |
 Porfiria SanchizDoctora Fedelman | Doctora Fedelman |
 Eduardo FajardoCapitán | Capitán |
 Ángel de AndrésToni | Toni |
 Rafael Romero MarchentEsteban | Esteban |
 Nerio BernardiEnrico De Paoli | Enrico De Paoli |
 Osvaldo GenazzaniJohn | John |
 Arturo MarínJefe tribunal militar | Jefe tribunal militar |
 Félix FernándezRecepcionista hotel | Recepcionista hotel |
 José FrancoMaitre | Maitre |
 José PradaMiembro tribunal | Miembro tribunal |
| MManuel AguileraTelegrafista | Telegrafista |
 Santiago RiveroCapitán | Capitán |