Preludium.

Theater props maker Karel Vajgant has a young wife, Magda, and two children, seven-year-old Pavlík and eleven-year-old Pepička. Magda is a caring mother, but she feels that her husband prioritizes work and his comfort. In a weak moment, Magda becomes unfaithful. Vajgant receives an anonymous letter that warns him of his wife's infidelity. His friend, the opportunist Tonda, advises him to throw away the letter and instead devote more time to Magda...