Music agent Ricardo (producer Abel Salazar of THE BRAINIAC) travels to a remote village to track down pianist Samuel Magno (Enrique Rambal) to make arrangements regarding a comeback performance. His trip is interrupted by the discovery of a crashed car and a mauled young woman. He seeks help at a remote hacienda but is refused and the young woman dies. The police believe her injuries were caused in the accident. Ricardo discovers that the hacienda he sought help at belongs to Magno who informs him that he cannot play anymore and only plans to conduct the orchestra and not perform himself but he has been training beautiful pianist Laura (Martha Roth) to make her debut during his performance. While Ricardo is staying in the village, Laura visits him and tells him that she is unnerved and that Magno does in fact still play the piano but only at night and always the same mysterious tune. Ricardo investigates and discovers the corpse of Alejandra (also Roth) in a shrine holding a piece of sheet music. Magno's mother sees him take the music and informs her son who we learn sold his soul to the devil to become the best pianist in the world and in turn had to murder pianist Alejandra and that whenever he plays the mysteriously bequeathed piece of music, he turns into a monster. In his monster form, he proves a threat to Laura since he feels that she will take his place as the greatest pianist and Ricardo (after tussling with the monster to get the score back) sets about exposing the monster with Laura's help on the night of the performance.

While several other Mexican horror films of the sixties have an thematic debt to the concurrent string of Italian gothic horror films and a stylistic debt to old Hollywood, THE MAN AND THE MONSTER does feel more like a forties Hollywood horror film (big studio not poverty row) German Expressionistic touches and its concert finale full of screaming extras. Like other Mexican horror pictures of this era, it is beautifully shot on gorgeously gothic studio sets but the plotting (not just the dubbing) offers unintentional laughs as do the special effects (Magno's transformation is performed through a series of mis-aligned lap dissolves and the end result looks like a Halloween monster mask and inspires hilarity rather than horror when he pulls off a Lon Chaney PHANTOM OF THE OPERA-esque turn into close-up. Magno's soul-selling flashback is replete with Expressionistic set design and angles but the expression worn by his present tense self in the overlapping still frame undercuts the drama and the film is not as lurid or grisly as some of the other entries of the time. That said, while we can predict what is going to happen, the music hall climax is suspensefully drawn out incorporating the rhythms of the music, the expressions of the actors, and the pace of editing wonderfully.