Plot

After SpongeBob's beloved pet snail Gary is snail-napped, he and Patrick embark on an epic adventure to the Lost City of Atlantic City to bring Gary home.

When SpongeBob SquarePants's pet snail Gary gets kidnapped by Poseidon and taken to the Lost City of Atlantic City, he and his best friend Patrick Star must go on a rescue mission to save him from the dastardly plan of Poseidon before it is too late.—Cynical Irish

When SpongeBob SquarePants' beloved pet snail Gary goes missing, a path of clues leads SpongeBob and his best friend Patrick to the powerful King Poseidon, who has Gary held captive in the Lost City of Atlantic City. On their mission to save Gary, SpongeBob and the Bikini Bottom gang team up for a heroic and hilarious journey, where they discover nothing is stronger than the power of friendship.—krmanirethnam

The Movie begins with a David Attenborough like sequence, introducing all the characters. Gary proceeds to wake up SpongeBob and he and Patrick yell good morning out their windows, annoying Squidward in the process. SpongeBob goes on to reminisce about all the good times they've shared together, before rushing off to work.

At the Krusty Krab, Squidward tries to ignore SpongeBob, but ends up getting burnt by the grill. Mr Krabs puts SpongeBob to work and the smoke from the grill lures customers in. Plankton watches the whole thing through a pay telescope and plots plan number 3,087 and Karen shows him the wall of failure, before saying that SpongeBob is the problem, but Plankton still believes Krabs is the one.

Sandy walks in with a robot named Otto, which Krabs hires and Otto fires him. Krabs throws Otto into Planktons trash and Karen hears the commotion and goes to raise Otto themselves. At closing time, Plankton goes to analyze the formula, before losing the paper, slipping on water, ending up through the potato slicer and into hot grease as he realizes SpongeBob really is the problem.

Meanwhile, in Atlantic City, King Poseidon admires himself, before noticing a wrinkle, getting a snail that runs out of slime and the Chancellor tells him they are out of snails, so the Chancellor writes a royal decree recommending a snail, which Plankton reads and gets rid of Gary to get rid of SpongeBob.

SpongeBob gets home and sees that Gary is gone and emotionally looks back at when he first met Gary at Camp Koral. Patrick walks in and shows SpongeBob the decree and SpongeBob says he doesn't have the courage to go and get Gary and Patrick says he'll go with him and the duo embark on a road trip, with Otto, but not without some miscommunication on the way. Unfortunately, SpongeBob and Patrick argue over what kind of trip it would be and the two end up crashing into a billboard. The friends forgive each other.

There is still trouble at the Krusty Krab, where the customers get hungry, Squidward can't operate the grill and he and Krabs get hurt.

SpongeBob and Patrick are now on land and debate being in a dream, before entering Goner Gulch and meet a tumbleweed named Sage, who gives them a "courage coin" and confirms they are in a dream. The two rush into the inferno saloon, without listening to Sages task for them. When they rush in, they see zombie cowboys, who begin dancing and Snoop Dog sings as El Diablo arrives and captures SpongeBob and Patrick in a cage. He gets angry and tells them they aren't in a dream, before SpongeBob and Patrick try using the coin, but nothing happens until they open the curtains, burning El Diablo to ashes and the Zombies are freed and the duo rush away from El Diablos ashes. Back underwater, Sage shows SpongeBob that Gary will be tortured if he doesn't provide slime for Poseidons face.

Plankton walks into the Krusty Krab to receive the formula and Mr Krabs gives him everything and Plankton says it doesn't feel as good as he'd hoped. Meanwhile, SpongeBob and Patrick arrive at Atlantic City and Sage tells them not to gamble, but they get distracted, gamble and ultimately wake up after crashing. Sage comes to see them and accuses them of not listening to him and reminds them of why they are there and Sage tells them that they woke up right on the steps of Poseidons palace and use a mobility scooter to create havoc inside. They end up on stage and perform a version of Pat a cake, before SpongeBob sees Gary and Poseidon tells him he renamed him Fred, before seizing SpongeBob and Patrick and putting Gary in glass.

Sandy rushes over to SpongeBobs house and sees he is missing, so she rushes over to the Krusty Krab to ask Squidward and Mr Krabs about where SpongeBob is and the news on the TV says SpongeBob and Patrick are to be executed and Sandy, Mr Krabs and Plankton go to rescue SpongeBob and Patrick and Squidward goes to see Kelpy G perform. Sandy extends the Patty mobile and ignites the vehicle, rushing to Atlantic City.

SpongeBob and Patrick are now in Prison and SpongeBob gives up hope, but Patrick says it's not over yet, before he reminds SpongeBob of the coin and he realizes that Patrick gambled the coin, but only because SpongeBob told him to and Patrick goes out and into another cell, before Sage tells them that the courage is inside him and things get way worse and the kings guards come and collect them.

The four friends arrive at Atlantic City and the execution begins the Chancellor is dressed as a judge and Patrick tells SpongeBob that he made a plea deal with the prosecution and it seems as if SpongeBob is about to die, until the gang show up and tell the audience about how they all met SpongeBob at Camp Koral, before Mr Krabs tells him he is the secret to the formula, through a song with the same title, before they all walk out as Squidward bows. King Poseidon notices they switched the real Gary for a cardboard cutout and Patrick stops for free food as the guards chase them down the hall. The friends pretend to be a knight and fight off all the guards, before Squidward slips and falls out the window and they rush down to save him, only to fail.

Otto comes to collect them, but gets trapped and Poseidon says he loved the entertainment and all will be forgiven if SpongeBob leaves Gary with him, but SpongeBob refuses. Poseidon then notices he never had any true friends and he begins to cry and SpongeBob says he will be his friend, in a similar way to how he became Patricks friend and SpongeBob tells Poseidon to let himself go and he does so. Poseidon salutes SpongeBob and allows him to keep Gary and he frees all the other snails.

Back in Bikini Bottom, everyone in town has a pet snail. The film ends with Bikini Bottom as a sea snail refuge.