Xena (Lucy Lawless) and Gabrielle (Renee O'Connor) come upon four prisoners being led by two bounty hunters. When Xena learns that the captured men are enemies of the hated Julius Caesar (Karl Urban), she overpowers the guards and frees them. Khrafstar (Marton Csokas), one of the released prisoners and the First Priest of Temple of the One God, explains to Xena that he is recruiting mercenaries to join the warrior Boadicea (Jennifer Ward-Lealand) in Britannia to fight Caesar. Xena immediately offers her help.
On board the ship, Xena tells Gabrielle that she and Boadicea were allies in Gaul long ago, but Xena betrayed her. She took control of her men and ordered her killed, but Boadicea managed to escape to Brittania. Just as she finishes her story, a Roman Centurion (Anton Bentley) comes aboard to announce that Caesar has forbidden any vessels to land on Britannia's shores. Xena publicly agrees to turn back towards Gaul, but takes the ship north instead, slips ashore and sends a message to Boadicea. By the time the Centurion and his soldiers arrive, realizing that they've been duped, Boadicea and Xena have joined forces to launch a furious attack on Caesar's men. The Roman soldiers are forced to retreat, but not before the Centurion takes Gabrielle and Khrafstar captive, unbeknownst to Xena.
The two women warriors, bound only by their mutual hatred of Caesar as far as Boadicea is concerned, head back to Boadicea's camp where the mercenaries are settling in. As Xena tries to find out the whereabouts of Gabrielle and Khrafstar, she is approached by a woman named Meridian (Catherine Boniface), a member of the Temple of the One God, who is also wondering where Khrafstar is. Xena soon realizes that they were captured during the battle and begins to devise a rescue plan. Meanwhile, Gabrielle and Khrafstar have been delivered to Caesar, who orders the Centurion and his soldiers to guard them for the night. Khrafstar tells Gabrielle more about his belief in the One God. Back at the camp, Xena and Boadicea are preparing their men for battle the following day.
By first light, Caesar has already learned that Xena is trying to lure him into a trap. He orders that a full legion of men be prepared for combat, at the same time, orders the deaths of Gabrielle and Khrafstar by crucifixion. The two are hauled up on crosses before the ground suddenly erupts. Xena, Boadicea and their men emerge from shallow "graves" and defeat the surprised Romans, freeing Gabrielle and Khrafstar. Caesar responds by ordering that every legion in the country be gathered to fight. Xena, meanwhile, plans her defense.
The two women warriors station their men high up on the seven hills surrounding the valley where Caesar expects the big battle to occur. Xena's plan is to force Caesar to divide his army and fight uphill. In order to secure the area, they take out the Roman soldiers guarding the Temple of the One God but do not destroy the temple itself, a decision which angers Ares (Kevin Smith) who considers the "cult" a threat to the Olympians. Meanwhile, an intrigued Gabrielle accompanies Khrafstar to the Temple of the One God. There, Meridian begins a strange invocation and suddenly, the circle of worshippers grab Khrafstar and Gabrielle, binding Khrafstar to the altar as a sacrifice. They then begin chanting praises to Dahak, an evil Sumerian god, as Gabrielle and Khrafstar struggle. Finally, Gabrielle manages to free herself but in order to save Khrafstar, she winds up killing Meridian with a dagger. Khrafstar becomes instantly calm and explains to Gabrielle that Dahak needed a sacrifice of purity and innocence, which she has just given him. As Gabrielle looks on in horror, he adds that she will be the one to allow The New Kingdom of Dahak to rule the world.
Outside, Xena and Boadicea notice the sky turning black and stormy over the Temple and Xena goes to investigate. There she finds Gabrielle with blood on her hands, lying next to the altar covered by Meridian's dead body. As a sobbing Gabrielle confesses to Meridian's murder, Khrafstar appears and thanks Xena for allowing Dahak, the Dark One, to rule. Xena attacks him and a brutal fight ensues. Meanwhile, the altar explodes into a ball of fire and collapses into a pit where the tendrils of flame capture Gabrielle, then shoot to the roof and suspend her over the pit. Khrafstar suddenly morphs into monster and renews his attack, screaming that he is the Deliverer. But ultimately, Xena is able to use his own rage against him and sends him into the burning pit. Leaping through the air, she saves Gabrielle from the flames and shields her body from falling debris as the entire temple collapses and takes on a familiar shape -- Stonehenge.
Guest Starring: Kevin Smith (Ares), Jennifer Ward-Lealand (Boadicea), Marton Csokas (Khrafstar), Meighan Desmond (Discord), Karl Urban (Julius Caesar), Catherine Boniface (Meridian), Anthony Ray Parker (Deliverer), Anton Bentley (Centurion), Patrick Kuhtze (Brit Guard), David Holton (Lieutenant), John Manning (Captain), Brad Homan (Jiela), Daniel Martin (Soldier), Andre Coppell (Squad Leader)
Starring: Lucy Lawless as Xena, Renee O'Connor as Gabrielle
Written by Steven L. Sears
Directed by Oley Sassone
Trivia: Dahak is the first of many manistifations of the Devil to appear on "Xena: Warrior Princess" and "Hercules: The Legendary Journeys".