The Alligator People (1959)

Newly married nurse Joyce Webster (Beverly Garland) doesn't know what to think when her husband, Paul (Richard Crane), disappears during a train ride. She hires private investigators and eventually tracks him to an old bayou plantation, where the owner (Frieda Inescort) insists she's never heard of Paul. Joyce sticks around anyway and soon learns that local doctor Mark Sinclair (George Macready) has been using a life-altering alligator serum on the town's residents, and that Paul is among them.