The spring of 98 AD is a time of optimism in the turbulent frontier province of Britannia. The season looks set fair for peace and prosperity, and business is brisk at Aurelia Marcella's inn on the road to York.

But soon a wagon arrives bearing a local farmer seeking treatment for a grievous sword wound. Before the farmer dies, he tells Aurelia his family is in grave danger and hints that her sister's family, living near him, is also threatened. Aurelia sends for her twin brother Lucius, who is a government investigator. Together they head for the eastern coast to investigate and to check out a shipwreck bearing valuable official cargo. A band of piratical Gauls is working the area—are they cover for something worse?

Then friction between native farmers and Roman settlers turns into open violence. Both sides resort to terrorist tactics, all building to a terrible climax at the annual festival for the sea god. Beneath it all flows a current of subtle, personal agendas....