: Two bosom friends decide to make an incubator to raise chickens. After spending a lot of work, the guys and their classmates bring nine chickens to the incubator and take them to the village.

After an unsuccessful test of a steam engine, two bosom friends Mishka and Kolya decide to make an incubator to raise their chickens. From the heap of old junk they make the machine and with the help of an electric lamp set the desired temperature. Having taken the eggs that the chicken had just laid in the village, the boys put them in an incubator and wait for the appearance of the chicks, a fun little family.

Around the clock, Kolya and Misha are on duty at the incubator, maintain the desired temperature and turn the eggs over. A classmate who came to visit Kostya Devyatov, they show the incubator and asked to keep it a secret. When the boys are at school, they are replaced by Mike, Misha's younger sister, who expects to receive a chicken as a present.

In the lesson, Kostya asks the teacher Marya Petrovna what an incubator is - the familiar boys made it at home. Talking about the incubator, Marya Petrovna says that the incubator can be made at home, but the guys should be disciplined, and not like, for example, Kolya and Misha.

Since the incubator is at Misha’s house, he hardly sleeps at night and sleeps on the weekend. Kolya, who came to him, paints Misha sleeping and brings an album with drawings to school, which causes laughter from classmates.Offended Misha offers Kolya to take the incubator to himself and also not to sleep at night. Now the guys are laughing at Kolya, who comes to the classroom, confusing his shoes.

Ten days have passed. Once, Kolya, from fatigue, does not hear the alarm ring, and the temperature in the incubator drops by several degrees overnight. He decides not to upset his friend, although he understands that to be silent is disgusting.

Interested classmates Kostya tells the news about his friends who made the incubator. Classmates admire unfamiliar boys, believing that Misha and Kolya are not capable of this.

Misha and Kolya grabbed the deuces, and the chairman of the council of the detachment assembly shamed them. To protect friends, Kostya says that it was they who made the incubator. Classmates offer help and make a watch list. They also help the boys draw on lost knowledge.

With the help of Marya Petrovna, the guys are preparing boxes of grass and food for hatched chickens. Finally, the long-awaited day comes, and all the guys come to look at the chicks, but there are no signs that chicks are hatching now. Feeling guilty, Kolya confesses to Misha his mistake, but he replies that he is guilty, because once through his fault the temperature rose very much. The guys are desperate that so much work was wasted, but then a crack appears in one of the eggs and the chicken’s beak is shown. Soon, other eggs begin to crack, and chickens appear in the incubator. Misha's calculations turned out to be wrong, chickens hatched on time.

On the birthday of the chicks, guys and Marya Petrovna come. One of the children brings a rattle, which newborns really like.

Of the twelve eggs ten chicks hatched, two embryos died. But soon another chicken dies, and Misha and Kolya take the remaining nine chicks to the village. In summer, the boys will come to them on vacation.