At a tavern, the Archangel Michael informs Xena and Gabrielle that the evil Roman emperor Caligula is now immortal and has embarked on a killing spree in his quest for ultimate domination. He appeals to Xena for help, insisting that only she, with her power to kill gods, can stop Caligula. Knowing that innocents are being murdered and fearing that her own daughter Eve, who is now in Rome, is in grave danger, Xena agrees to help.   In Rome, a crazed Caligula hands his sword to a priest who drives it through his gut to prove his immortality to the crowd. Suddenly, a commotion erupts and an openly defiant Eve is thrown in front of Caligula praising the god of Eli. Moments later Gabrielle, disguised as Cynda of Thrace, appears and announces the arrival of the great female gladiator Mosca, who has traveled from Gaul to pay homage to Caligula. When Caligula orders his men to open the gates, Mosca/Xena, clad in a glamorous costume and gold mask, charges towards him in her chariot, knocking his men aside in the process. Excited by a challenge, Caligula races his chariot towards her and before he knows what's happening, Mosca/Xena flips through the air, lands in his chariot and puts a knife to his throat. But before she can stab him, Ares lunges out of the crowd and tackles Mosca/Xena, informing her that if Caligula dies, so will his sister Aphrodite. After Ares and Eve are hauled off to the dungeon, Caligula turns to Mosca/Xena and demands an explanation. Cynda/Gabrielle quickly jumps in, insisting that Mosca/Xena was simply challenging him to a race for the chance to appear before the supreme lord Caesar. Intrigued, Caligula invites the women to a party at the palace that night. In their quarters later that evening, Xena instructs Gabrielle to go to the party and try to figure out the connection between Aphrodite and Caligula while she pays a visit to Eve and Ares in the dungeon. As the festivities unfold, Gabrielle casually tries to question Caligula and Aphrodite. Down in the dungeon, Ares informs Xena that Michael came and took Eve. When she inquires about the bond between Caligula and Aphrodite, Ares reveals that his sister has become Caligula's sex slave and has agreed to a union that links their lives that can only be broken if she forsakes him or if Caligula is unfaithful. When Mosca/Xena enters the party, Gabrielle informs her that Aphrodite has no memory of them or her past. Xena realizes that Caligula, in leaching off Aphrodite's immortality, has also sapped her memories. Moments later, a cage holding Ares is wheeled in and Aphrodite orders Mosca/Xena to kill him. Mosca/Xena first teases Caligula, kissing and biting his lip before approaching the cage and grabbing Ares him by the hair. As Caligula watches, his lip suddenly begins to bleed. Terrified that he's losing his immortality, he has Mosca/Xena apprehended and clears the room. He instructs his guard to stab him and is enormously relieved when nothing happens. Meanwhile, Gabrielle corners Aphrodite and reduces her to tears in striving to spark her memory. Back in the main room, Mosca/Xena tells Caligula that she is the Celtic goddess of sex with the power to kill gods and wants to join forces with him. When she offers to take Aphrodite's place, Caligula refuses, leaving her to remove her chains herself which she does with ease. The next day, Caligula enters the main room and finds Mosca/Xena gone. The Archangel Michael suddenly appears and tells Caligula that Mosca has requested that Caligula kill Eve with his own hands. Manipulating Eve as bait for Xena, Michael convinces Eve to return to the palace, ostensibly to deliver the message of Eli to the emperor. As she bows before Caligula, he raises a dagger to kill her, but stops when Mosca/Xena enters and knocks Eve unconscious. Convincing Caligula that he needs her more than Aphrodite, Mosca/Xena tells him to toss Eve in the dungeon with Ares. Back in Xena and Gabrielle's quarters, Michael materializes and is prepared to kill Aphrodite, claiming she's lost her immortality. Xena bursts in and she and Michael struggle. Gaining the upper hand, Xena is about to stab him when a brilliant light freezes her and she collapses. When Gabrielle rushes to her side, Xena reveals that Eli has just taken away her power to kill gods. As Xena and Michael argue, Aphrodite suddenly regains her memory and forsakes her relationship with Caligula. All now believe the connection has been broken, rendering Caligula mortal once more. Meanwhile, Caligula, excited to show Mosca/Xena how he plans to display his immortality to the masses, summons her to watch as a guard thrusts an axe into him. Xena is naturally stunned when he remains unscathed, and soon learns that Aphrodite has completely lost her immortality and Caligula has absorbed it. The next day, Mosca/Xena enters the town square, ties a bound Eve to a post, and takes the podium to announce that she and Caligula will engage in a deathmatch chariot race. If Caligula wins, he gets to kill Eve and if Xena triumphs, she gets to execute Caligula. Cornered, a shocked Caligula boards his chariot and the two battle furiously during the race until Caligula finally loses control and wipes out. The crowd goes wild as Mosca/Xena is about to shove her sword into the emperor, but at the last moment she hands the sword to him. To avoid total dishonor, Caligula takes his own life. DISCLAIMER Gabrielle's undercover disguise was severely harmed during the making of this motion picture.