Plot
A community of land hermit crabs living beneath a New Jersey beach boardwalk often plays host to a group of sea hermit crabs who come onto land for vacation, and the two species cannot stand each other. Armen, a timid land crab, is reluctant to go out and socialize due to the way his parents died in a storm when he was a child. His rotting shell, inhabited by a fun-loving organism named Anemone, is the only reminder of them.
Three muscular crabs, Armen’s friends Bobby, Manny, and Jimmy, drag him to a club owned by his uncle Bruno. There, the crabs get into a fight with an arrogant sea crab named Mako when Armen inadvertently bumps into Ramona, a tourist sea crab he had fallen in love with earlier. The land crabs are evicted as a result, and a frustrated Armen leaves on his own.
While sulking by the seashore, Armen is confronted by Mako and his goons, who hassle him and steal his shell. Ramona intervenes, but she and Armen are swept away by a high tide that devastates the land crab civilization.
Armen ends up at the far end of the beach above the boardwalk, where he is captured by a human collector and given an artificial shell to be sold as a pet. He soon reunites with Ramona, and together they escape and work their way back home. During their journey, they share their insecurities: Armen’s fear of doing anything beyond staying in his shell, and Ramona’s desire to escape her overbearing mother, Val, who expects perfection from her.
Armen and Ramona’s disappearances intensify the rivalry between the land and sea crabs, largely because Mako fabricates a story claiming Armen tried to steal Ramona from him. Bobby begins second-guessing his tendency to use physical force against his enemies and soon encounters Ramona’s deaf sister, Shelly, who is searching for Ramona. When Bobby walks her home, Val sends him away. Later, when he tries to break up a fight between his friends and Mako’s gang, he accidentally snaps off Mako’s right arm.
Mako vows revenge and falsely claims that Armen is dead, presenting Armen’s shell and a shell-shocked Anemone as proof. The land crabs declare war.
As Armen and Ramona fall in love, two crabs they met at the pet shop begin judging their relationship, making Armen hesitant about his feelings, much to Ramona’s distress. Eventually, Ramona begins to dehydrate and collapses. Armen carries her toward the water, pushing past the fighting land and sea crabs, who stop battling when they see Armen risking everything to save her.
Ramona awakens, kisses Armen, and together they return to the surface. Armen is praised for his heroism, Mako is exposed as a liar, and the land and sea crabs work past their differences. Mako gives Bobby a new shell as a peace offering, and Armen gives his own shell to a younger crab who needs it more.
