The Wood Demon (1974)

A luncheon party gathers to celebrate a wealthy unmarried man's birthday; his sister hopes he'll marry Sonya, the daughter of a selfish gout-ridden old professor who makes life Hell for his son George and his young wife, Helen. At the luncheon is Khrushchov, a passionate environmentalist, called "the Wood Demon" by all, in love with Sonya and she with him, but neither will say it. Two weeks later there's a family meeting at the professor's estate; two weeks after that, a supper at the cabin of Dyadin, who's cheerful to all. George, Helen, Sonya, and Khrushchov are each suffocating. Can any of them take action?