Led by Commander Marcus Artorius Agricola, the five thousand soldiers of Rome's Ninth Legion are legendary for their aggressive fighting skills and superb leadership. The Legion is stationed in Britannia in the year AD 122, and Rome sends them north of York to subdue the unruly Pict tribes.

But when they arrive, the unthinkable happens. They are routed and forced to flee toward the coast, ending up at a Pict holy place. Here, the entire Legion is mysteriously teleported to England at the beginning of World War II. The terrified men suddenly find themselves pursued from the air by "flying crosses" and on the ground by a relentless crew of British soldiers.

The Legion flees to Crail, Scotland, trying to come to grips with their new reality. They discover that one of the Picts, a vicious holy man named Mormaer, has time-traveled with them. Worse, he is quickly learning the ways of this new world and won't hesitate to use his deadly knowledge against his enemies.

When the Legion discovers that they are right in the path of another invading force-the Germans-they know they will continue to do their duty and defend Great Britain. But their shields and swords are no match for this era's technology. What's more, with Mormaer waiting to strike, the Legion may not survive what could be their last battle.