Aided by a sea Captain, Pac-Man attempts to transport a large shipment of power-pellets across the Pac-cific ocean. The shipment is cleverly disguised as a barge of garbage being towed by Pac-Man's tugboat, but Mezmaron is not fooled and has been following in a submarine. He launches the Ghost Monsters from the torpedo tubes, and they chomp a hole in Pac-Man's boat, which quickly fills with water and begins to sink. The Ghost Monsters' celebration is cut short as they realize the barge is still attached to the sinking tugboat, and they are also pulled under the sea along with the barge of power-pellets.
The boats descend to the bottom of the ocean and settle to the ground in Paclantis, an undersea city protected by a huge protective air bubble. Pac-Man, the Captain, and the Ghost Monsters are captured by a squad of Paclantean guards and brought before the Queen of Paclantis. The Queen is excited to learn she has captured the famous Pac-Man. She orders her captives taken to the dungeon and declares that the next day Pac-Man and the Ghost Monsters will engage in a chomp chase in the arena.
The jailed Pac-Man seems resigned to his fate, but the plucky Captain points out there's a way to escape. He loosens a stone in the floor. Pac-Man brightens up and they begin to tunnel their way out. Meanwhile, the Ghost Monsters are also growing antsy in their cell and hatch their own escape plan. Using a tuna sandwich as bait, they lure the guard with a fishing pole, and when he bites, they reel him in and swipe his keys. Once free, the Ghost Monsters try to make a break for it.
However, the paths of both groups of escaped prisoners lead straight to the arena, filled with cheering Paclanteans. They've accidentally arrived just in time for the Queen's chomp chase. The contestants are fitted with gladiator gear. Pac-Man complains that the Ghost Monsters have an unfair advantage since he and the Captain don't have any power-pellets, but the chomp chase begins, and the Ghost Monsters quickly go on the attack.
Pac-Man and the Captain run for it, but it's not long before they're cornered. Pac-Man has one chance to fight back and tosses a net over the Ghost Monsters to pin them to the ground. But the tactic backfires when Pinky simply inflates to a size large enough to dislodge the net. He tosses it back at Pac-Man and the Captain who fall to the arena floor, trapped under their own net. The Ghost Monsters pounce on Pac-Man and the Captain and chomp them, draining their energy and leaving them wilted and helpless.
The Queen declares Pac-Man to be the loser, but the Ghost Monsters are not done chomping and they go after her. The Paclanteans scatter in terror as the Ghost Monsters begin chomping them in a rampage.
Meanwhile, Mezmaron has found Paclantis in his submarine and honed in on the fallen shipment of power-pellets. He deploys a claw from the bottom of his sub which penetrates the air bubble and locks onto the power-pellet barge. The Captain alerts Pac-Man about what's happening, and Pac-Man resolves to stop Mezmaron. Pac-Man lassos the barge with the net, and though he and the Captain are still saggy and woozy from getting chomped, they manage to find enough collective strength to pull the power-pellets loose. The terrified Queen stops running for her life as the power-pellets rain down, and she gobbles them up along with the other Paclanteans. Pac-Man and the Captain are revived, and everyone works together to chomp the Ghost Monsters. The Ghost Monsters' eyes zip to Mezmaron's submarine and activate the controls. Despite Mezmaron's angry shouting, they turn the sub around and flee from Paclantis.
Somewhat humbled by her close call with the Ghost Monsters, the Queen thanks Pac-Man for saving Paclantis. She offers Pac-Man her daughter's hand in marriage as a reward. The Queen removes the Princess' veil revealing her to be comically homely and clearly smitten with the heroic Pac-Man. Pac-Man nervously stammers that he's already married and runs off as the Princess chases after him.