No te engañes corazón (released in English as Don't Fool Yourself Dear) is the first full-feature film of Cantinflas after becoming a star of the carpa circuit (folk theater). It was also one of the earliest films of Sara García and Carlos Orellana and the first where they share the screen. Don Boni (Orellana) is diagnosed with a deadly disease and decides to spend his last days doing good deeds. He leaves his wife and decides to help people. He then gets drunk and wakes up with a winning lottery ticket and realizes that the doctor who diagnosed him has been sent to prison for fraud.

In a Gothic-styled monastery, a monk named Javier sees the face of another monk, Juan, and suddenly attempts to bludgeon him to death with a heavy crucifix. Both men then relate their own versions of a story of romantic rivalry between them.

Alfonso, Eduardo and Cristina get lost when visiting a forest. A strange monk finds them and takes them to an ancient convent. There, the three amigos suffer personality changes, specially Cristina who tries to seduce Alfonso in a strange coincidence to a story told by an old monk. After some efforts to escape, Alfonso is trapped inside a jail and more strange and macabre situations happen.

Carlos, a young man from a good family, falls prey to the drugs offered by drug dealer El Bruite. In despair, his fiancée Laura tries to help him fight his addiction. At the same time, bandits are robbing and kidnapping the region's wealthy.

Adolfo, a railroad engineer, is sent to a provincial station to investigate a series of thefts from trains. The investigation uncovers the existence of an unknown gang, led by a man named Ruby, who finds ways of committing their crimes in broad daylight. Director García Moreno received the full cooperation of the National Railroad in the making of the film, and it still stands today as a document of the great technological advances made in Mexico during the 1920s.