Entertaining Mr. Sloane (1970)

Sloane, a handsome, sexy and completely amoral young man, joins Kath's household as a lodger and proceeds to manipulate her and her brother, Ed. He is recognized by Kemp (Dadda) as the murderer of Kemp's former employer, whereupon Sloane murders Kemp. Sloane's "just desserts" are not what one would expect. imdb