[1][2] Events are narrated from the perspective of 15-year-old Sasha Akimov, centering on three resistance zones holding out against the protracted German siege.

Sasha Akimov, a 15-year-old musician, and his older brother, Andrey, whose parents were killed in the Spanish Civil War, are serving in the 333rd Rifle Regiment of the Red Army at the Brest Fortress.

Elsewhere, a commissar, Yefim Fomin, discovers he is unable to bring his family to Brest due to a shortage of train tickets.

During the fighting for the East Fort, Junior Lieutenant Andrey Akimov (brother of Sasha) is killed while destroying two Panzer IIIs with a 45 mm anti-tank gun, helping Gavrilov repel a German attack.

He reveals that the Red Army is retreating toward Minsk and Fomin realizes that the men must leave the fortress or die.

The next morning, realizing he can't properly defend them, Kizhevatov reluctantly orders the surviving civilians (including his wife and daughter and also Sasha) to vacate the fortress during a cease-fire.