Bad Penny (1978)

Penny Hickey (portrayed by Samantha Fox) is named as the recipient of a rich uncle's estate if she can solve a puzzle as to it's whereabouts. She must locate "Sydney", a friend of the uncle to find the solution to the puzzle. Naturally, her uncle knew many "Sydneys", and each one asks her for favors before giving her their answer to the puzzle. Meanwhile, Celeste, her evil sister, plots to eliminate her so she can solve the puzzle and get the inheritance herself.