Tras la sangrienta conquista de Camuloduno, durante el crudo invierno del año 44 d.C. el ejérctio romano se prepara para extender la invasión de Britania con un contingente de 20.000 legionarios armados hasta los dientes. El general Aulo Plautio confía en que la llegada de la primavera facilite la campaña, pero, inesperadamente, su familia es raptada por los druidas de la Luna Oscura.

En el verano del año 43 d. C., la invasión romana de Britania se encuentra con un obstáculo inesperado: la desconcertante y salvaje manera que tienen los rudos britanos de enfrentarse a las disciplinadas tropas imperiales. La situación es desesperada, y quizá la inminente llegada del emperador Claudio para ponerse al frente de las tropas en la batalla decisiva sea el revulsivo que unos legionarios aterrados y desmoralizados necesitan.

Britain 43 AD: after a series of bloody battles, Camulodunum (modern-day Colchester) has fallen to the invading Roman army. The Emperor has returned to Rome, leaving the fearless Centurion Macro and his young Optio, Cato, to rest and regroup, along with the rest of the Second Legion. But trouble is not far ahead and as their noble leader General Plautius plans the next phase of their campaign, word arrives that the ship carrying his family to join him was wrecked in a storm off the south coast. His wife and children have fallen into the hands of a dark sect of Druids, who now demand the return of those of their brotherhood taken prisoner by the Romans. Unless their demands are met within one month, Plautius's family will be burned alive. Will Cato and Macro discover where the Druids are hiding their hostages? Can they find some way to rescue them before time runs out?