Slim is a boy whose astronomer father is visiting the country estate of an important industrialist. The industrialists son, Red, has found two strange animals, and he enlists Slim in a plan to turn the animals into a circus act. The astronomer, meanwhile, tells the industrialist that he has been in contact with space aliens who want to open up their world to interstellar trade. Their world needs help, the astronomer says; ever since the atomic wars that destroyed their old civilization, the world has been regressing. Unless something is done, their culture may be facing total collapse.
When they dont hear from the aliens, the astronomer and the industrialist go out looking for them. They find a small crashed spaceship with a number of tiny dead aliens in it, and the astronomer is convinced that the aliens all died in the crash.......
Youth is unusual in that none of the characters are given names, or physical descriptions until the very end. All the adults, including the two humans, are known by their professions, and the two young aliens are known by their nicknames. This is necessary to preserve the twist at the end, but it has the effect of giving the story a certain artificiality compared to Asimovs usual style.