Retired history teacher Charlie is looking for a new project but gets a lot more than he bargained for when he finds his new shed is possessed by the spirit of Gustin, a young apprentice druid from the first century AD. Gustin persuades Charlie to come back in time to Roman Britain, where he wants his help investigating why he died. This extraordinary trip becomes yet more intense when they come across a secret youth organisation led by Gustin's childhood friend.

Central Britain has been at peace since Boudicca's revolt some forty years before but now his group is plotting another rebellion. The elders are alarmed, most are prospering under Roman rule and they'll try to stop their frustrated offspring in any way they can. Charlie is horrified when he realises that he has something the rebels badly want, all he wants now is to get back to his own time, where his family have only just discovered his disappearance. A nerve-shredding sequence of adventures follows, which finally culminate in the most dramatic discovery of all back in the 21st century.