The Crooked Hearts (1972)

While the police investigate the latest in a series of mysterious disappearances of older women, they are led to a matchmaking service run by Mrs. Stanton where the last victim was a client. Meanwhile, the service's newest client, Laurita Dorsey, begins a relationship with Rex Willoughby, an elegant gentleman she met through the service. But neither Laurita nor Rex are exactly who they appear to be.