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.
A woman is told his military husband is considered dead, the truth is he has been transferred to the secret service. When he returns to Spain and they get reunited he ends killing a German spy, and then she gets prosecuted.
A newly remarried widow is accused of having murdered her first husband, who died from arsenical poisoning. Being her present husband a lawyer he takes charge of her defense.
A woman returns home from a mental hospital, to find his husband has used her case to write a play.
The strange disappearance of the dogs of his neighbors leads Juan to investigate the case on his own. It ends up finding out that the author of the robberies is a young woman called Eloísa, the cocky daughter of a scientist who uses dogs to create an antidote against sleep. Juan and Eloísa fall in love, but he will ask her to leave her luxurious mansion to live only with his salary.
