Witek runs after a train. Three variations follow on how such a seemingly banal incident could influence the rest of Witek's life. One: he catches the train, meets an honest Communist and himself becomes a Party activist. Two: while running for the train he bumps into a railway guard, is attested, brought to trial and sent to unpaid labour in a park where he meets someone from the opposition. He, in turn, becomes a militant member of the opposition. Three: he simply misses the train, meets a girl from his studies, rerns to his interrupted studies, marries the girl and leads a peaceful life as & doctor unwilling to get mixed up in politics. He is sent abroad with his work. In mid-air, the plane he is on explodes.