Akishin is initially rejected due to poor health but is allowed to join the project thanks to the intervention of an old Bolshevik, Uncle Seryozha.

However, he is falsely accused of sabotage by the mine's leadership, who blame him for the previous accident and the mysterious disappearances of Ufimtsev and Max, a German anti-fascist.

Lyolya, receiving a letter from Ufimtsev through a returning comrade, rushes to the meeting and clears Kaitanov’s name with the support of the workers.

As World War II begins, Kaitanov is sent to the front, and Ufimtsev is assigned to train pilots in the rear, despite his pleas to join combat.

Amid German air raids on Moscow, Lyolya shelters with her son and a young woman, Tanya, who confesses her love for Ufimtsev.

Meanwhile, Kaitanov reflects on Akishin’s love for Lyolya through a letter recovered from the submarine, and Ufimtsev secretly resumes his passion for aviation.