When an attempt to bring Peter and Kate back to their own time is bungled, Peter finds himself stranded in 1763 while The Tar Man, a villainous eighteenth-century criminal, returns with Kate to twenty-first-century London.

Ignored by his father and sent to Derbyshire for the weekend, twelve-year-old Peter and his new friend, Kate, are accidentally transported back in time to 1763 England where they are befriended by a reformed cutpurse.