The Black Widow (1951)

Mark Sherwin ( Robert Ayres) is the victim of a brutal beating and car theft. The thief dies in a crash; Mark suffers from amnesia, and recuperates on a horse-training property. Discovering a clue, he returns home to find he had been declared dead, his wife welcomes him back, only to plan a real death for him so she and his best friend (with whom she is having an affair) can get his substantial wealth.