After the sudden tragic death of her father, young Nadinka was left a complete orphan. She also lost the home where she lived her entire life. Now she has only her faithful nanny Agasha and her beloved little Sergeichkа. Sergeichkа, Sergey Il’ich—he’s completely absorbed in an especially important project: he’s working on the construction of the world’s first nuclear icebreaker “Lenin,” which so rarely calls from Leningrad. And poor nanny Agasha doesn’t really believe in the existence of her fiancé, because she’s never seen him. But now to life’s objective difficulties for young people are added problems created by ill-wishers: talented engineer Sergey, with his innovative ideas, is declared a saboteur. Who and why needs this persecution? And will the young couple be together?