A Matter of Diamonds (1968)

Riley Walker arrives at an Italian villa with an injured hand; he had cut his hand whilst attempting to get into the neighbouring villa belonging to his aunt. He introduces himself to the residents and stays until his aunt, Mrs Panzack, returns. Speaking to his aunt it is revealed that the visit was a ruse to meet the occupants of the house and in particular Maggie Brown, who is in possession of some diamonds they are interested in.

Unfortunately the movie A Matter of Diamonds is not yet available on HBO Max.