Perry Mason - Season 2 Episode 13
The Case of the Borrowed Brunette

Eva Martell is hired out of numerous candidates by Melvin Slater to impersonate a woman named Helen Reynolds. Eva is paid extremely well and given a nice apartment to live in with her Aunt Agnes as long as she continues with her impersonation. Both Eva and her aunt suspect a rat and seek Perrys advice. Then Melvin Slater turns up dead in the apartment.