Barcelona, Spain. A young man is murdered in the middle of the street in front of the police headquarters. Miguel and Marcial, two agents of the Criminal Brigade in charge of the investigation, find in the victim's room a newspaper where a cryptic classified ad appears.
| Actor | Role |
|---|---|
 Conrado San MartínMiguel | Miguel |
 Elena EspejoCarmen | Carmen |
| TTomás BlancoAntonio | Antonio |
 Manuel de JuanMarcial | Marcial |
 Luis Pérez de LeónDon Rafael | Don Rafael |
 Carlos Muñoz ArosaRafael | Rafael |
 Guillermo MarínEyewitness | Eyewitness |
 Casimiro HurtadoPascual el Mirada | Pascual el Mirada |
 Emilio FábregasPolice Commissioner | Police Commissioner |
 Eugenio TestaJulián Azores | Julián Azores |
 Marta GrauDoña Lola | Doña Lola |
 José GoulaPostmaster | Postmaster |
| RRicardo FuentesNot listed | Not listed |
 Modesto CidPhotographer | Photographer |
 Rafael NavarroPrologue Narrator (voice) (uncredited) | Prologue Narrator (voice) (uncredited) |
 Xan das BolasNot listed | Not listed |
 Carlos RondaPolicía | Policía |
 Miguel Ángel ValdiviesoVendedor de periódicos | Vendedor de periódicos |