Crimson, also called The Man with the Severed Head, and whose Spanish title means “The Rats Don’t Sleep at Night”, is a Spanish-French crime drama masquerading as a horror film via a left-field plot twist about a partial brain transplant. It stars Spanish horror icon Paul Naschy, billed as Paul Nash, and hails from a golden era of horror cinema. Don’t get excited yet.
Gangster Jack Surnett (Naschy) is about to open a jewelry store’s safe when the greed of one of his henchmen accidentally triggers the alarm. Surnett is promptly shot in the head by police, and a drunken doctor (ubiquitous character actor Carlos Otero) suggests—wait for it—taking him to an old friend who’s working on brain transplants. That surgeon and his equally surgical wife (Silvia Solar, radiating warmth and intelligence) need a freshly decapitated head, so the gang picks a rival gangster (Roberto Mauri) known as The Sadist—the decisions just keep getting smarter—whose tendencies will naturally start taking over the patient.