Season 1 Episode 16 - Mortal Beloved

While Xena and Gabrielle are eating in a Tavern, one of the girls working there reports having seen a ghost outside. Xena goes out and finds the ghost of her dead lover Marcus waiting for her. He starts to tell her of a terrible change in the underworld, but before he can finish some dark figures appear to drag him off and they all disappear. Going with Gabrielle to the place he mentioned before he was dragged off, Xena dives into a lake and swims to the bottom where she finds her way through some caves to the river Styx.

Going across, she discovers that the evil- people have taken over the Elysian fields and thrown those who should be there into the underworld. Finding Marcus, they proceed together to a castle where Hades, is imprisoned having had his helmet of invisibility stolen. Xena and Marcus discover that a psychopathic murderer has stolen it and has plans to invade the world of the living. Xena and Marcus swim to the top of the lake and stop the killer and take the helmet back to Hades.