The script can be read here but below is a synopsis.
Hapless prisoners reach through the bars of the Prison of Agony as it pans out to show the prison suspended on chains above an active volcano.
Venger instructs his giant servant Karrox to escort a dwarf who betrayed him into the prison but Karrox has a conscience and refuses. Venger conjures an image of Karrox's homeland and shows it demolished by an earthquake caused by Venger's sorcery, making it clear that if Karrox disobeys him then the earthquake will happen. Areluctant Karrox apologises to the dwarf and escorts him to the prison.
Meanwhile in a jungle clearing the heroes wake Bobby with a surprise birthday and give him presents. Eric has collected a box of little green ball creatures that hop away. Laughing, Bobby and Uni chase after them. Soon after the remaining heroes are ambushed and captured by Lizard Men.
Bobby and Uni return to find Dungeon Master. He explains that his friends have been taken to the Prison of Agony and as a birthday present gives Bobby an amulet, claiming that it will protect him from Venger, before adding that its power is in the giving and not the keeping. He points Bobby in the direction of the prison before disappearing.
The Lizard Men present the captured heroes to Venger who takes their totems and has them imprisoned.
Meanwhile, Bobby approaches some volcanoes and comments that he cannot see a prison. The image of Dungeon Master appears on his amulet and tells him that it is in the biggest volcano.
In the prison the heroes mull over their situation until an elated Eric thinks he sees Dungeon Master but it is just a monstrous prisoner who looks like him from behind. Recoiling in horror from the misidentified Dungeon Master he bumps into another monstrous prisoner who asks, "you must be... lunch?"
Bobby spots two Lizard Men cross an intervening river on a raft. When they have gone he and Uni steal the raft and punt across to the biggest volcano.
In the prison the heroes are befriended by Strongheart who tells them they can escape. Rolling a Santory 1855 barrel away he reveals a missing brick in the wall behind it. Strongheart and the heroes escape the prison and clamber along the chain suspending it but are spotted by Lizard Men who release a slimebeast that chases them back inside the prison.
Bobby and Uni reach the other side of the river but are spotted by Lizard Men. Climbing up the volcano Dungeon Master's image appears on the amulet and reminds him that the amulet will protect him from Venger's sorcery. While Bobby is looking at the amulet the image disappears and he sees a Lizard Man behind him in its reflection. He battles and defeats the three Lizard Men who demand the club.
Further up the volcano Bobby is confronted by Venger and Karrox. Venger demands the club and fires a mystical bolt at Bobby but it is absorbed harmlessly by Dungeon Master's amulet. Astonished, Venger commands Karrox to grab the club instead, reminding him that he can destroy his homeland when Karrox shows reluctance. Bobby and Uni manage to escape and lower the drawbridge to the prison.
Karrox catches up with them but in the skirmish falls over the side. Bobby pulls him up and in gratitude Karrox formulates a plan where hides the club, telling Venger that it had fallen into the lava, and escorts Bobby into the prison before secretly handing the club back to him. Karrox then tells the heroes that he will lower the drawbridge at midnight and Bobby gives him his amulet, so that the giant will be protected from Venger. The other heroes lament the loss of their totems but Strongheart suggests he knows where they are hidden as he had a magical weapon, a golden hammer, confiscated by Venger too.
At midnight Karrox lowers the drawbridge and Bobby smashes free from the prison with his magic club. The Lizard Men raise the drawbridge but this only results in the fleeing heroes and Strongheart sliding to safety with the drawbridge sealed behind them, preventing the Lizard Men from pursuing them.
They reach the dungeon where the golden hammer is kept. Bobby smashes down the locked door and they enter but although Strongheart's helmet and golden hammer are there, the heroes' totems are not. A wall explodes and behind it is Venger plus five Lizard Men, each with one of the heroes' totems.
Battle commences but the Lizard Man with Presto's hat conjures a bird that swoops down and grabs the golden hammer from Strongheart's grasp, leaving only Bobby and his club to protect them.
Karrox arrives and grabs the totems from the Lizard Men and returns them to the heroes, much to Venger's annoyance who summons a two-headed lava dragon. The dragon corners Strongheart who despairs about not having his hammer. Diana remedies this by throwing her javelin at the bird, dropping the hammer into Strongheart's grasp. The lava dragon breathes fire at Strongheart but his magical hammer's forcefield protects him.
Presto conjures a fire hose and douses the dragon, defeating it. Venger disocunts the victory saying that they cannot survive the volcano's explosion, which he presumably has engineered.
Karrox grabs Venger but the two are jettisoned outside the volcano in a globe of light that serves as Venger's escape pod. The heroes flee the prison and outside meet Venger and Karrox who have just landed. Venger is furious at Karrox's betrayal and fires a mystic bolt at him but the amulet Bobby gave him relfects the bolt, knocking Venger over the edge and into the lava. Venger teleports before being incinerated.
The volcano is about to erupt and consume the prison suspended above it so Hank fires an arrow that lowers the drawbridge, allowing the prisoners to flee. Karrox helps the dwarf he earlier imprisoned as recompense. The volcano explodes, destroying the prison, and the Venger's spectre rises from the volcanic ash and angrily tells them that "you will all pay for this," before dissipating.
Karrox returns the amulet and laments the impending destruction of his homeland. Bobby returns the amulet saying that Venger's sorcery won't be able harm him or his homeland.
Eric comments that giving presents on your birthday is bad policy. Dungeon Master appears and suggests that he should not accept the present that Bobby gave him; his freedom from the Prison Of Agony.