In the middle of the night, SpongeBob is having a nightmare while chattering his teeth. After SpongeBob wakes up from the nightmare, he hears a noise down in his kitchen. SpongeBob is frightened about that noise. He now tries to call for help, and realizes that his telephone line is cut, and now puts on his army helmet then grabs his tennis racket. His knees are still shaking as he runs to open up the door, and slides down to the library. SpongeBob now trips on his toy truck, and falls down the steps. He runs into his kitchen, and finds novelty teeth chattering. He then finds his fancy boot hoping around, and yells "Hey, knock it off!" Then smacks the boot with his tennis racket which leads him to smack his face. SpongeBob now drops his tennis racket, and karate chops the boot, unaware that Gary is hiding in his fancy boot. Gary now comes crashing out of the boot, and spins around, then finally a bucket and some soap come down on Gary. When SpongeBob takes the bucket off Gary, he now finds that Gary has soap in his mouth, and manages to take it out now hearing Gary's gasps. SpongeBob thinks for a minute that Gary is not hurt, and then he touches Gary's shell, it breaks. SpongeBob now apologizes to Gary. Gary meows, smells his own stink, feels pain, and begins to cry. SpongeBob grabs Gary and tries to hug him, but Gary now goes up to the ceiling in more pain. Then, SpongeBob tries to find out how to fix Gary's shell, first by taping it back together but it breaks again.
in the bedroom where SpongeBob goes through his trunk to find solutions for Gary, he first finds his Hawaiian shirt but realizes it does not work, but then finds his Christmas Santa hat but realizes that it's too last season, and later finds his gorilla mask that he needs for Halloween. SpongeBob first finds his copy of his pants, and tries them on Gary but it gets wet and drops. SpongeBob finds his space helmet by trying it on his head, and then Gary but realizes it doesn't look right. SpongeBob later finds his race car helmet, and puts it on Gary now realizing that Gary rocks. Gary then throws it and shows him a Shell Spiffy which is a magazine full of snail shells. Gary meows at SpongeBob to take a look at page 72 which features his old shell with a lot of new features, and the cost was 9,595.95 Dollars. SpongeBob wonders where he can get a high quality shell without spending a fortune. Gary knows where to get a shell really cheap, and shows SpongeBob a commercial which now features Scooter cleaning up his snail's broken shell, which is for Angry Jack's Shell Emporium, where the prices are always very cheap. Angry Jack now introduces himself, and advertises a commercial full of shells which includes a refurbished plastic shell, and gets angry with the numbers in his face, and then the other shells.
Angry Jack starts talking about selling for real. When SpongeBob and Gary get there, they interrupt Angry Jack in the commercial. He now apologizes to Angry Jack thinking that he is going to get angry for real. Angry Jack reveals that he just does it for the commercial to make them loud and better. Jack then finds a shell that looks exactly like Gary's old one, and tries it on Gary which makes him very happy. SpongeBob thinks it's perfect, and wants to buy it for Gary because it looks just like the old one. The shell then slides off Gary and breaks which makes him depressed. Jack then decides to try a different shell on Gary. But SpongeBob wants to take it, and decides to make sure that it's put down by pushing down on it harder. He now manages to break it, and makes Gary mad at him again. He manages to grab another shell but accidentally breaks it over Jack's face. SpongeBob now manages to grab another shell off the shelf but trips over his shoe laces, and breaks it. Jack now hands over Gary to SpongeBob in order to take care of the shells, and tries on the reflective model on Gary. The reflection blind both SpongeBob and Gary. After being almost blind, SpongeBob accidentally starts to break all of the million shells. Jack now gives SpongeBob one more shell which is proven indestructible. SpongeBob now makes sure that his hand and shoes are perfect, and wraps them up in bubble wrap and tape but the shell manages to slip through the bubble wrap, and breaks not like a shell. SpongeBob mentions about reducing inventory which makes Jack angry for real, and demands immediate payment. SpongeBob hands Jack some quarters, and Jack demands one arm and legs, also a heart and one eyeball, and his pants.
But SpongeBob is now walking, while carrying Gary wishing that his shell would grow back, and then finds a square cardboard box in front of a dumpster, he draws on it, and it becomes Gary's replacement shell. But unfortunately, Gary is more depressed and he and SpongeBob both break down in tears. Mr. Krabs comes out from the dumpster and that's when SpongeBob has an idea. SpongeBob now wants Mr. Krabs to help him find a new shell for Gary. Mr. Krabs manages to shake SpongeBob upside down to find some money to help Gary get a new shell. Mr. Krabs now starts to walk away but SpongeBob manages to make a deal to work for free for the rest of the year. Mr. Krabs now wants to cut SpongeBob's health insurance. SpongeBob makes the deal.
That night at SpongeBob's house, he has another nightmare while his teeth are chattering again. He turns on his flashlight, and sees Mr. Krabs' shell on Gary. However, he sees Mr. Krabs coming in through the window very cold, and wants to borrow a blanket. After giving Mr. Krabs a blanket, SpongeBob manages to smart off his mouth to Gary about the shell. Then, Gary once again annoyed locks SpongeBob outside and turns off the light.
If one looks closely, after SpongeBob breaks all the million shells in the store, one shell falls from the ceiling that looks like Gary's shell and another shell that looked like Gary's in the broken shell pile.
The title comes from the term "shell shock," which is the result of stress from battle as well as a term used in various Teenage Mutant Ninja Turtles series.
Angry Jack demanding one of SpongeBob's arms and legs may be a reference to the term, "I'd give an arm and a leg for ________.
When SpongeBob is putting on the space helmet, his arms go through the helmet.
In some scenes, Gary's purple slime on him disappears.
When Angry Jack presents SpongeBob the last shell available, he claims that it is "certified indestructible," but when SpongeBob gets the shell, the shell breaks from simply falling from a foot above the floor.