Forced to stay with his childless aunt and uncle for the summer holidays while his brother convalesces from measles, Tom Lang is lonely and bored. The only fascination he has is with an old grandfather clock that stands in the hallway, the property of Mrs. Bartholomew, the owner of the house. The only thing Tom knows about it is that he must never touch it. Lying in bed unable to sleep one night, he hears the clock strike 13. Creeping downstairs to investigate whilst the rest of the house sleeps he throws open the back garden door and crosses the threshold into a magical Victorian garden of the 1880s.