While jellyfishing in Jellyfish Fields, SpongeBob and Patrick encounter an object sticking out of the ground. They decided to dig it up, and they discover an old submarine. Meanwhile, at the Krusty Krab, Squidward and Mr. Krabs think of an idea--to bring the Krusty Krab to the customers. SpongeBob and Patrick drive the submarine into the Krusty Krab, which makes Mr. Krabs have SpongeBob and Patrick take the submarine and sell Krabby Patties to the passersby. Seeing this, Plankton gets upset since he had the idea years ago. He takes the fist of the Chum Bucket and uses it as a mobile Chum Bucket.
SpongeBob and Patrick are unsuccessful with their first customers, so SpongeBob offers to pay them to take the Krabby Patties, which they agree to. Meanwhile, Plankton attempts to sell food to a child, whom he then insults out of impatience. All of a sudden, the child's parents, great grandmother, Harold, and even Jack M. Crazyfish start throwing rocks at Plankton. Soon, the mob runs out of rocks, but since Patrick wasn't paying attention to the Krabby Patties, they burned and hardened. SpongeBob and Patrick are able to sell the burnt patties to the mob for them to throw, and the two friends head off.
Later on, SpongeBob and Patrick fall into an abyss and wake up a ginormous sea monster who has been asleep for the past 79 years. Starved after his hibernation, the monster purchases 640 Krabby Patties. However, just as SpongeBob and Patrick are running out of patties, Plankton's Chum Bucket vehicle comes crashing into the submarine. Chum squeezes through the cracks of the submarine, so SpongeBob and Patrick decide to use the chum to make the burgers, which the monster ends up enjoying even more than the Krabby Patties. Plankton sees the sea monster hand SpongeBob and Patrick giant dollar bills in exchange for the chum burgers, and he attempts to get the monster to refuse the food. However, Plankton is mistaken for a chocolate éclair and the monster chases him away. Meanwhile, because they are down in the abyss, SpongeBob and Patrick have to let go of all the money they have earned to float back up. Instead, they bring back 37,000 pounds of decorative undersea rocks, much to Mr. Krabs' disappointment.
In the English version, the monster said he didn't eat for 79 years, but in the Netherlands version, he said 97 years.
The salesman from Chocolate with Nuts returns in this episode and cons SpongeBob and Patrick one more time, this time without even trying as they hand him money for trying some Krabby Patties. It seems like he remembers SpongeBob and Patrick since he says "Hey, thanks AGAIN guys." He is also shown to be married.
Running gag: SpongeBob drives the submarine and bumps into the Krusty Krab, destroying the window.
This is one of the episodes to have bubbles in a title card.