A Neanderthal child is brought to the present day as a result of time travel experiments by a research organization, Stasis Inc. He cannot be removed from his immediate area because of the vast energy loss and time paradoxes that would result. To take care of him, Edith Fellowes, a children's nurse, is engaged.
She is initially repelled by his appearance, but soon begins to regard him as her own child, learns to love him and realizes that he is far more intelligent than she at first imagined. She names him 'Timmie' and attempts to ensure that he has the best possible childhood despite his circumstance. She is enraged when the newspapers refer to him as an "ape-boy". Edith's love for Timmie brings her into conflict with her employer, for whom he is more of an experimental animal than a human being.
Eventually, her employer comes to the conclusion that his organization has exacted all the knowledge and publicity which could be gotten from Timmie, and that the time has come to move on to the next project. This involves bringing a Medieval peasant into the present, which necessitates the return of Timmie to his own time. Miss Fellowes fights the decision, knowing that he could not survive if he went back to his own time because he has acquired modern dependencies and speech. She decides to smuggle the boy out of the facilities, but when that plan fails, she causes the integrity of the Stasis module to fail and returns to the ancient past with Timmie.