Following the death of their miller father, his eldest son inherits the mill, the middle one a donkey, and the youngest a cat. While initially disappointed, the lad soon learns not only that the cat can talk but is quite resourceful.
El Santo, the masked Mexican wrestler, investigates a series of kidnappings. He discovers that the mysterious Doctor Caroll is using the victims as part of his experiments to develop an army of monsters. Naturally, El Santo is able to overcome them all - with wrestling!