In a village, the ground cracks open, letting out an eerie light and smoke. Not far from it, a couple of drunks finish a drinking song. One of them then promises to do it; the other tells him not on his boots. The first drunk clarifies his statement by saying he plans to pledge his love to a girl. The second drunk asks what'll he do if he pledges his love to the girl's sister. The first drunk hopes that the sister is just as pretty.

The two stumble upon the crack in the ground. The first drunk approaches it, intrigued. He's suddenly caught in a strange force, and begs his friend for help. The other drunk wanders over, places his hands on his friend's shoulders, and becomes stuck as well. The two scream into the night as they become charred statues.

Elsewhere, a young woman is bathed in milk and clothed. A screen shot of her face shows a woman on a mission. An item that catches the eye is the blue medallion around her neck.

The ancient Greek version of Don King arrives in a village, challenging the men of the village to fight a flabby old man named Eryx the Boxer. The fight promoter promises a payoff of three-to-one if someone defeats Eryx. A villager bets he can defeat Eryx, and his friends place money on him as well. The man enters the ring, ready to fight the old man, when the fight promoter tells him that he paid to fight Eryx the Boxer. The villager is aware that he has just been tricked, as a man who literally stands a head above everyone else enters the ring; this is Eryx the Boxer. Eryx easily puts the villager out for the count forever. The promoter challenges the dead villager's friends to fight Eryx; all of them die at Eryx's hands. An old villager tells a boy to go find Hercules.

Meanwhile, Hercules' two sons, Klonus and Aeson, are hunting something in their father's cornfield. They hear growling, see a lion, and attack. They don't make any headway, but Hercules' daughter, Ilea, smartly whacks the lion in the head. Hercules emerges from the lion's skin, enjoying himself.

In the distance, the boy from the village arrives, seeking Hercules' help. He quickly follows, and discovers that Eryx has killed most of the men in the village. Hercules condemns Eryx for his actions, and Eryx responds by saying he needed something to do. Hercules fights Eryx, but is apparently outmatched. Eryx uses Hercules for a human punching bag while Zeus tries to give advice to Hercules from the sidelines. Hercules decides enough is enough, and storms back, belting Erxy until he is disoriented. Hercules kicks the back of Eryx's knee, and the giant falls over backwards onto a sharpened stake that holds the ropes for the boxing ring. The fight promoter approaches Hercules and tells him that he's won a prize: a peacock feather, compliments of Hera. Hercules takes it, and angrily throws it on the ground.

Outside the village, Hercules goes to one of Hera's temples, and says he's tired of fighting her. He asks for a truce, and Hera declines by sounding a thunderclap. Angry again, Hercules tears down her temple.

On the way home, Zeus asks why Hercules tore down Hera's temple, saying it will make her angrier than before. He also asks for Hercules to go to another of Hera's temples and perform a small sacrifice, which Hercules refuses to do. They talk about how hard Hercules' life has been, and Zeus tells Hercules that he will have to work hard to keep everything he's worked for. Hercules agrees, and says it's worth it. Hercules tells Zeus that he should visit him sometime, and Zeus promises to. As they part ways, Zeus offers some more boxing tips to Hercules.

The next morning, Hercules is working on a metal harness. He can't get it right, and asks Nessus what the problem is. As Nessus appears from behind the stables, it's clear that he is a centaur. Nessus tells Hercules that iron cannot be bullied into shape. Hercules goes to a window and watches his children play, and is so intent on watching them that Nessus has to bring Hercules back to reality.

The girl who appeared earlier in the movie approaches Hercules' house. Hercules goes out to meet her, and the girl collapses in his arms. She says her name is Iole, and asks Hercules to help her village, Gryphon. She says that a hole opened in her village, spewing death. Deianeira comes outside, and tells Hercules to bring Iole inside.

That night, Nessus is in the local tavern, disgusted at all the praise Hercules receives. When the patrons don't stop toasting Hercules, Nessus interrupts them. He questions how great Hercules really is. Nessus says that Hercules is never around, and that he has to take care of Deianeira. A patron tells Nessus to shut up, but Nessus doesn't flinch. He tells everyone that Hera protects him, not Hercules, and leaves.

Deianeira sits with Iole in her temporary bedroom. Iole asks Deianeira if Hercules will help her. After a moment, Deianeira says she thinks he will. Iole gasps, then tells Deianeira that she saw something outside the window.

Going out into the night, Deianeira hears the sound of metal hitting metal. She walks into the barn and sees Nessus working on Hercules' metal harness. Finished, he presents it to her, and tells her that Hercules couldn't do it better than he could. Deianeira says that's okay with her, and tries to leave, but Nessus blocks her exit. He asks her if she really trusts Hercules going out on a trek with the young, beautiful Iole. Deianeira slaps him across the face, and tells him to sleep it off.

In the morning, Hercules comments that the weather is suitable for traveling. He senses that something is wrong with Deianeira, and she says that she will miss him. Just before Hercules and Iole leave, Iole takes off the blue medallion around her neck to show her thanks and gives it to Deianeira as a present. Deianeira refuses to take it, but Iole insists, and Deianeira relents. Hercules and Iole then leave, accompanied by Nessus.

While Deianeira shops in the market later in the day, an old woman stops her. The old woman tells Deianeira she's sorry about her husband. Deianeira doesn't understand, and the old woman tells her that the medallion around her neck came from a Nurian maiden. These young women, she says, can persuade a man to do any task for them, even die. Deianeira doesn't believe the old woman, but the old woman produces some evidence: she holds an identical medallion in her hand and presents it to Deianeira. Deianeira is shocked, and runs away, dropping her basket.

Back at home, Deianeira takes her oldest son, Klonus, aside, and tells him that she is leaving for a while. She also instructs him to obey his aunt, Althea, and take care of his younger brother and sister. Klonus says he will, and then Deianeira kisses him on the cheek and leaves.

Hercules asks Nessus if the river they need to cross is any shallower at his end. Nessus says it isn't, and Hercules says he will go find Iole. He finds Deianeira confronting Iole about her being a Nurian maiden. Hercules calms her down, and says he knew Iole was one when she arrived. He tells her that everything will be all right, and sends her home with Nessus to guard her.

After Hercules crosses the river, Nessus tries to abduct Deianeira. He grabs onto her cloak, but Deianeira manages to free herself from it. Nessus says that only he deserves her, and tries to go after her again. Deianeira screams for Hercules, and Nessus tells her that Hercules can't help her. He doesn't know that Hercules does hear Deianeira, though, and Hercules fires an arrow that hits Nessus in the back of his neck.

As Nessus begins to die, he asks Hera why she didn't protect her. As his blood stains Deianeira's cloak, he receives some insight from Hera. Nessus tells Deianeira that if Hercules puts on the cloak stained with his blood, Hercules will remain forever faithful. She's rather doubtful about this, but takes the cloak.

By the time Hercules arrives, Nessus is already dead. He comforts Deianeira, and tries to send her home again. She resists, then offers Hercules her cloak (the blood stain is gone). Hercules tells her that when he puts it on, he'll think of nothing but her. The two then part ways.

Hercules and Iole stop by an inn for something to eat. Inside, they find a man tearing up the inn. Hercules asks the innkeeper what happened. The innkeeper says he doesn't know; the man started eating his soup and then went wild. Hercules picks up the club and prepares to attack the man when Iole stops him. She approaches the man instead of Hercules, walking slowly and talking in a gentle voice. She approaches the man, and convinces him to stop the destruction. She then looks at the ruined form of a table and sees a steaming bowl of soup, and knows what happened. Iole tells everyone that the man burned his mouth on his food and needed water but he cannot talk. The innkeeper offers a jug of water to the man, which the man gulps down. Iole walks past an astonished Hercules out the door.

They continue to travel, unaware that they are being followed. Next morning, Iole decides to go swimming in the nude. She hears some rocks move and scolds Hercules for looking at her. In reality, it is the pursuer looking at her. Hercules is minding his own business when the pursuer attacks Hercules with a spear. Hercules is bewildered at the unexpected attack, and breaks off the spear point. The attacker flips a switch and the other end of the spear turns into a pitchfork. Hercules breaks it off too, and sends the attacker to the ground. He holds a hand above the man's head when Iole appears. She tells Hercules to stop; she knows the man. His name is Castus, she says, and he loves her, but it is not meant to be as he is not part of her destiny. Hercules brings down his fist in a different location, and knocks Castus out cold. They pack up and leave.

Hercules and Iole see Gryphon from a difference, and Iole says the hole is worse then before. The inhabitants of Gryhpon have all moved out of the town, which Hercules enters. An old woman approaches Iole and tells her she knows what is going to happen if Hercules fails.

Hercules finds the hole in the ground, and stands on the edge of it. Zeus appears next to him, and Hercules asks where the hole leads, and Zeus tells him it goes straight to the underworld. Hercules then asks Zeus if he is mortal. When Zeus hesitates to answer, and angry Hercules demands that Zeus tell him. Zeus sighs, and says that Hercules is mortal; he can die. Hercules thinks it's a trick to keep him out of the hole, and Zeus retorts that he has a family now, and to go home to them.

In Iole's tent, Castus is trying to get Iole to admit her own feelings for him, but Iole refuses, saying that any relationship with him is not part of her destiny. Hercules approaches, and Castus hides. Hercules tells Iole that he can't do anything; he has a family now, and has to live for them. Iole tries to change his mind by offering herself to him. Hercules refuses, and Iole says then she'll jump in the hole. Hercules tells her it's a suicide mission, and Iole retorts saying she's already dead since she failed in her mission. He says he's sorry, and tells the hiding Castus to take care of Iole, then leaves.

It is now night, a rather chilly one, and Hercules puts on Deianeira's cloak. It seems to come to life, strangling Hercules and forcing him to the ground. After a brief struggle with it, Hercules throws it to the ground. The cloak changes into a peacock, and Hercules looks to the sky to see Hera's eyes looking down at him, and then they disappear. Hercules screams that the gods will never stop, and jumps into the hole.

Deianeira has returned home when a messanger from Gryphon runs up. He says that Hercules put on a cursed cloak which drove him mad. His only escape was to jump into the hole. Deianeira grieves over the message, saying the cloak was to protect the both of them.

After a long fall, Hercules falls with a thud on the bottom, in the underworld. He starts to walk around when Charon the boatman arrives. Charon takes a good look at Hercules, and refuses to take him across. Hercules asks why not, and Charon says because he's still alive. Hercules lifts Charon off the ground, and asks about making an exception, which Charon happily agrees to.

As the boat glides over the river Styx, a thunderous bark is heard. Hercules asks what it is, and Charon tells Hercules that Cerberus has broken free and is terrorizing the underworld instead of keeping the dead in the underworld. As they reach the other side, Hercules leaves without paying Charon, and then takes Charon's lamp as well. As Hercules pushes Charon's boat back out onto the river Styx, Charon complains about how he gets no respect. Hercules continues on, finds Cerberus' broken chains, and then walks through a portal. Hercules disappears, and the lamp he carried falls to the ground.

Back in the real world, Deianeira stands on a cliff thinking about her life with Hercules. As she ponders this, and image of Hercules appears, beckoning her to join him. She closes her eyes and walks off the edge of the cliff to her death. After she jumps, a peacock feather hits the ground where she took her last step.

In the underworld, Hercules awakes. Three seductresses approach him, asking Hercules to free them with a kiss. As they try to seduce him, Hercules retreats into flashbacks of romantic times with Deianeira. When he wakes up, he sees they are really ugly ghouls who have used their serpent tongues in an attempt to kill him. He breaks free and knocks all of them out. More of the same kind of ghouls try to attack him, and Hercules climbs a vine to escape.

Hercules emerges onto a volanic plain with steep cliffs and lava seas (obviously Tartarus). He starts to walk when he runs into a group of old enemies he had killed, including Eryx the Boxer. Hercules tells one of them that Eryx had killed his mother. The man is incensed and attacks, only to be easily defeated. Another warrior is reminded that the man Eryx just took out was his best friend, and so he attacks with the same result. The dead warriors begin to attack one another, and Hercules attempts to escape, only to be blocked off by Eryx the Boxer.

Eryx had come to Tartarus with the piece of boxing post he was impaled on still in him, and Hercules takes it out. Eryx is shocked by the hole left in him, and Hercules hits Eryx's knee with the post. Eryx is forced to fall in a fire, and he runs screaming in pain off a cliff into the lava below.

As Hercules continues on, he runs into Nessus, who is laughing maniacally. Nessus asks Hercules how he liked the cloak; it was all Hera's idea. Hercules reminds Nessus that he is dead, while he (Hercules) is alive and has a wife and family. Nessus tells Hercules that Deianeira is dead and in the underworld. Hercules doesn't believe it, and Nessus shows him a picture of it, telling him she's in the Elysian Fields, far from Tartarus. The picture disappears, and Hercules breaks down. He asks Nessus to show the picture again, and Nessus does, just because it causes Hercules pain. Unexpectedly, Hercules jumps through the picture and to the Elysian Fields.

In the Elysian Fields, Hercules meets two women who look like Deianeira but aren't before finding her. He is shocked when Deianeira says she doesn't know him at all. Hades appears, saying that he removed the misery that brought Deianeira to suicide. Hercules says he will take Deianeira with her. The thunderous barking is heard again, and Hades tells Hercules he has no time for arguements. Hercules realizes there may be one way for Deianeira to return, which Hades agrees to: bring back Cerberus, and Deianeira is free to go.

Hercules is trying to find Cerberus when he finds Hades' hunters, or rather a pile of body parts that belong to the hunters (who are all dead). The hunters piece themselves together again, and see Hercules. They tell them they don't need him. Hercules leaves to find Cerberus himself. Hercules and the hunters converge again after a nice long chase, in which Cerberus is forced into a pit. Hercules jumps into the pit, but has a change of heart. He drops his weapon (to the hunters' amazement), and approaches Cerberus much like Iole approached the man in the tavern. To everyone's astonishment, Cerberus responds to this, and before much longer, Hercules is chaining Cerberus back to his post at the entrance to the underworld.

Deianeira joins Hercules there, and in a few seconds, the two find themselves back in Gryphon, where they see the hole sealing itself up. Iole apologizes to Deianeira, and says that she and Castus will start their own family. Deianeira tells Iole that she'll do just fine. As their eyes meet, Hercules and Deianeira kiss.

Back at home, Zeus visits his favorite son. Zeus plays with Ilea while asking Hercules if he still cares about his mortality. Hercules says he doesn't; everything he wants is here now. The peace is not to last, though. A young man runs up the path to Hercules' home, saying that he needs Hercules.