Smiles of a Summer Night

In the lat 19th-century, a slightly-aging and totally amoral actress invites to her country-house party two married men---a lawyer and a count---who have both been her lovers in the past. She also asks them to bring along their wives. She has plans on taking one of them away from his present wife, but also ensure that all her guests leave paired up. The math doesn't work out until an uninvited guest also shows up.