It's 1940. German forces are prevailing over Allies across Europe. The crew of the Polish submarine, now serving in the Royal Navy, is waging a heroic fight against the invisible enemy.

A chorus rehearsal. Karol and Henryk are among the soloists. Like most of the singers, the two men lead the pretty quiet lives of senior citizens. They have been a couple for years, but no one outside their apartment knows about it. One day, they receive an invitation that shakes their meticulously hidden everyday life.