The main character is Tycho Tithonus, an 11-year-old boy. Each child in his family is named after a famous artist or scientist and their parents expect them to live up to their names. Tycho himself is named after Sleator's younger brother, who in turn, was named after Tycho Brahe, the Danishastronomer. He finds a pocket sized time machine in the family's garden. He immediately uses it to change some things from the past and to visit the future. But as he travels more and more he realizes that he is turning into something horrible and it becomes a race against time to save himself and his family from his own future self.