After the execution of the spy Mata-Hari, the secret service takes the opportunity to arrest some of her collaborators. To arrest one of the ringleaders, they use his girlfriend Niní, a naive dancer. The girl, tired of being manipulated by everyone, decides to become agent X25.
Nouveau-riche industrialist returns to Spain after 20 years in Mexico and discovers that his adopted son wants to marry into an aristocratic family and is trying to disguise his family history. Meanwhile, the young man's birth mother also shows up, and....
