After a brief dream sequence, Ivan Bondarev (Nikolai Burlyayev), a 12-year-old Russian boy, wakes up and crosses a war-torn landscape to a swamp, then swims across a river. On the other side, he is seized by Russian soldiers and brought to the young Lieutenant Galtsev (Evgeny Zharikov), who interrogates him. The boy insists that he call "Number 51 at Headquarters" and report his presence. Galtsev is reluctant, but when he eventually makes the call, he is told by Lieutenant-Colonel Gryaznov (Nikolai Grinko) to give the boy pencil and paper to make his report, which will be given the highest priority, and to treat him well. Through a series of dream sequences and conversations between different characters, it is revealed that Ivan’s mother and sister (and probably his father, a border guard) have been killed by German soldiers. He got away and joined a group of partisans. When the group was surrounded, they put him on a plane. After the escape, he was sent to a boarding school, but he ran away and joined an army unit under the command of Gryaznov. Burning for revenge, Ivan insists on fighting on the front line. Taking advantage of his small size, he is successful on reconnaissance missions. 

Детство 12-летнего Ивана закончилось в тот день, когда у него на глазах фашисты расстреляли мать и сестренку. Отец мальчика погиб на фронте. Оставшись сиротой, Иван уходит в воинскую часть и становится неуловимым разведчиком. Он с риском для жизни добывает для командования бесценные сведения о противнике. Но однажды он не вернется с задания.