Atti is a Roman teenager with ‘Atti-tude’, a smart kid who likes to bend the rules. When one of his schemes (selling horse wee as gladiator sweat) falls foul of Emperor Nero, Atti is forced to join the army and is sent to miserable, cold, wet Britannia. There the natives are revolting, quite literally, as Boudicca, Queen of the Iceni tribe, takes on the might of Rome.

As Atti’s legion are on the march, he is kidnapped by Orla, a feisty teenage Celt, who wants to prove to her father that she can be a Celtic warrior. When Orla’s grandmother, Brenda, is then captured by an enemy tribe, Atti seizes on the moment to save his own skin by persuading Orla that he can help rescue her grandmother. Working as a team, Atti creates a sleeping potion to knock out the opposing tribe and returns victorious with Brenda, only for the tribe to thank the Celtic Gods for her safe return by bidding to sacrifice Atti. But Orla can’t allow her new friend to die and so volunteers to carry out the execution; letting him free at the last minute.

Meanwhile Boudicca has united a number of Celtic tribes, ambushed the ‘undefeatable’ Ninth Legion and er… defeated them. Nero explodes, demanding that his remaining troops destroy his great nemesis. The only problem is the Celtic hordes outnumber the Romans 10-1. The Romans need a plan and quick. Atti rejoins his troops and uses his smarts to suggest a way to trap Boudicca's forces in a natural bottleneck. The Celts fall into the trap and Atti, now realising that there could be a slaughter, races to save Orla and her family.

The Romans win a memorable victory. After the Celts surrender, Atti has the option to return to Rome as a hero but he doesn’t wish to leave Orla and so settles into her village and helps the Celts modernise their lives the Roman way.