Torsh has fathered two sons who are so much alike that his parents cannot tell them apart. They grow up loving the same woman, Gwynellen. When it comes time to marry, the brothers fight over Gwynellen and nearly kill one another. Jason, the wise one, decides that they should both marry the wench and save both their lives. He will soon be off to join the Roman army. His brother, Julius, will stay on the farm. Jason convinces Julius that he will get the best of the deal since he, Jason, will be away most of the time. Only when he returns home must Julius relinquish the lady. They plan a most clever marriage.
Jason becomes a Roman volunteer and is so good with the groma ( a surveying tool) that his superior takes steps to make him an engineer and a citizen of Rome so he can become a true Roman soldier. Jason becomes friends with Silvius, a Roman with property in Roma. Jason is well known for his engineering skills and is the architect of the siege at Masada. The two men become friendly with Boudica, the Druid priestess who rules the Iceni. Jason falls in love with Thea, who is Boudica’s daughter. When the great uprising comes, Jason has to make a serious decision as he stands over the pregnant Thea with his upraised sword. She holds a spear to his midsection.
Over time Silvius becomes more and more corrupt and Jason begins to dislike him. Silvius is a womanizer and can be brutal to women. After the death of Silvius’ uncle, the two men travel to Rome. They see his vineyards, the opening of the Coliseum and even the eruption of Mount Vesuvius. They are covered in ash and dressed as civilians when they are captured by some Roman soldiers and put aboard a trireme, chained to oars. When a former officer recognizes Silvius, he is freed, but Silvius out of spite, does not tell his liberator that Jason is aboard as well and is a noted engineer.
Jason suffers on and eventually escapes when another officer recognizes his battered body. His Irish spirit cannot handle the confinement aboard ship and he has made his captors angry with him. They have beaten him viciously. Eventually, after service in the Holy Land, Jason returns to England and his own people. He wants to celebrate samhain with some former friends at their village. He makes the mistake of offering a scale model of a siege engine to the chief. He takes offense and Jason is injured. He must resign the Roman army and return to his home. His brother still lives there, but strange things happen when he realizes that Gwynellen knows of their little plan of deception all along.