Yesterday's Leningrad schoolgirl Masha Yablochkina, after a fierce blockade winter of 1941-1942, comes to the railway courses hoping to survive and gain strength. From there, the girl is sent to the construction of the Shlisselburg highway, which connects the city with the mainland and is in direct sight of German artillery. So the heroine gets into the 48th locomotive column of the special reserve NKPS, which, at the cost of the deadly risk, will have to deliver 75% of all cargo and military equipment to Leningrad.