Atti is a Roman teenager with brains but very little brawn. When one of his clever schemes falls foul of Emperor Nero, Atti is forced to join the army and is sent to miserable, cold, wet Britain where the natives are revolting - quite literally.

Things go from bad to worse when Atti is captured by Orla, a feisty teenage Celt desperate to prove herself as a warrior. After narrowly avoiding a very sticky end in a bog, Atti uses his Roman know-how to help Orla save her gran, who's been kidnapped by a rival tribe. Meanwhile a furious Nero is determined to crush the rebellion, led by Boudicca, Queen of the Iceni.

Atti rejoins his Roman troops and discovers they are preparing for an historic showdown with the Celts at the Battle of Watling Street. Atti's brains could save the day but they could also spell disaster for Orla as the two new friends find themselves lined up on opposite sides of the battlefield.