Determined to obtain the powerful Sword of Hera, Arciana (Katie Wolfe) and some fellow inmates break out of prison. Hercules (Kevin Sorbo) and Iolaus (Michael Hurst) join the search after they are approached by a guard who tells them that Arciana was last seen heading towards Mycenae. While on the road, Hercules and Iolaus encounter "Serena" (Sam Sorbo), but Hercules quickly realizes that she is not the real Serena. She explains that she is actually 'Sin' and governs a domain of evil souls that Hades has thrown out of Tartarus. She tells Hercules that the evil Xerxos (Jeremy Roberts) has escaped from her world and that it would take the two of them working together to send him back. Hercules declines and as "Serena" disappears, she tells him that Xerxos is headed towards Mycenae. While Hercules and Iolaus continue their journey, Hercules tells Iolaus that Xerxos was sentenced to death at the age of sixteen for murdering his parents. After he broke out of jail, Hercules brought Xerxos back to be executed and now Hercules thinks that Xerxos has returned to take his revenge. Suddenly, Hercules and Iolaus hear ungodly screams coming from the forest. They find Xerxos massacring the prison guards searching for Arciana. Hercules tackles Xerxos, but Xerxos proves stronger than he expected. Vowing to continue his murdering spree, Xerxos disappears. "Serena" materializes and tells Hercules that the blood of many innocents will be on his hands if he doesn't accept her help. Feeling he doesn't have a choice, Hercules agrees and "Serena" kisses him to give him the power to defeat Xerxos.
Before Hercules and Iolaus continue their trek, "Serena" tells them that Arciana is Xerxos' sister who escaped from the house the night her parents were murdered. She is bitter about her upbringing in orphanages and Hercules knows that she will take her anger out on the world if she gets her hands on the powerful Sword of Hera. "Serena" disappears and Hercules and Iolaus continue to look for Arciana. But Iolaus notices that Hercules' behavior is changing. Instead of just wanting to return her to prison, Hercules wants to kill her because she is related to Xerxos. As they continue walking, Iolaus can see the violence welling up inside Hercules and he convinces his friend that "Serena" has poisoned him. Hercules knows Iolaus is right and tries to control himself. "Serena" and Xerxos secretly witness this and "Serena" tells Xerxos to lead Hercules around until he takes a life in anger, which would condemn his soul to her domain. In return for his help, "Serena" promises Xerxos that he can see his sister.
Meanwhile, Hercules' condition worsens. He becomes so angry with Iolaus that his face morphs demonically. Iolaus leaves Hercules to search for Arciana by himself. He finds her in one of Hera's temples, but she already has the sword. Just as Arciana is about is about to kill Iolaus, Xerxos appears and stops her. Arciana becomes terrified when she realizes that Xerxos is her dead brother. She runs down a passageway and Xerxos follows. Hercules, now totally possessed, arrives at the temple and is about to follow Xerxos, but Iolaus grabs the sword and tries to stop him. Hercules breaks the sword in half and throws Iolaus aside. Xerxos catches up with Arciana in another chamber and explains that, unlike her, he was born evil. He grabs her skull and a flurry of hellish images pass through her head. Xerxos tells her that it's not too late for her to save herself. Hercules bursts into the chamber and he and Xerxos battle like demons from hell. Hercules is about to crush Xerxos with a gargoyle, when Iolaus runs into the chamber. Hercules makes direct eye contact with his best friend and it finally registers what he's about to do. Hercules' face returns to normal and he tosses the gargoyle aside. "Serena" appears and demands that Hercules finish off Xerxos, but Hercules refuses, knowing this is all a trap. Before he and "Serena" return to their realm, Xerxos takes one last look at Arciana and knows that she will change her ways. Feeling Arcinia has suffered enough, Hercules decides not to return her to prison.
Starring: Kevin Sorbo (Hercules), Michael Hurst (Iolaus)
Guest Starring: Jeremy Roberts (Xerxos), Katie Wolfe (Arciana), Sam Sorbo (Serena), Bill Florian (Head Guard), John O'Leary (Gravetender), Dennis Hally (Headmaster), Syd Mannion (Hera Priest), Tony Billy (Con #1), Des Wallace (Con #2), Danny Phillips (Hera Worshipper), Kerynn Walsh (Villager), Siaosi Fonua (Smithie #1), Slade Leef (Smithie #2), Kurt Holsted (Young Xerxos), Gerry Eller (Xerxos' Mother), Michael Phillips (Magistrate)
Written by Paul Robert Coyle
Directed by Mark Beesley
Trivia: The original plan for this episode was to have Hudson Leick reprise her role of Callisto. The storyline would have been exactly the same, except it's Callisto who comes back to save her sister from becoming evil like her. The plan was axed when Hudson's "Xena: Warrior Princess" commitments conflicted with the tight shooting schedule that "Hercules: The Legendary Journeys" had for its final eight episodes.