On a hunt for the legendary queen conch shell, 8 year old ARTHUR and his grandfather ZACHARIAH stumble upon an eight-foot-long Mako shark, dead on the beach with a fishing rope embedded around its neck. Zachariah informs Arthur that the shark is dead, but Arthur wants to resurrect it.

Arthur brings the shark (whom he named Jasmine) back home and dumps her in his kiddie pool. The first of his experiments begins: Arthur sneaks through the kitchen in search of his mother SELINA'S (33) table salt, but she catches and interrogates Arthur. Arthur does not elaborate on why he needs the salt, which makes Selina suspicious. For now, she drops it, telling Arthur about his upcoming play date with neighbor child PATRICK (9), and sets the table for breakfast. Arthur does so in a hurry, desperate to get back to Jasmine. He rushes to the backyard and dumps the entire salt container into the pool, waiting for Jasmine to come to life. Only Patrick has arrived, and so Arthur must 'socialize' with him. Patrick and Arthur have breakfast and a heart-to-heart about the permanent extinction of the dinosaurs. However, watching Patrick voraciously eat his breakfast, Arthur gets another idea. Arthur shows Patrick his dead pet shark and lets Patrick play with her. Selina relaxes on the hammock until she hears Patrick's blood-curdling squeals. Rushing to the backyard, Selina discovers Arthur trying to feed Patrick to the Mako shark. Patrick runs away, and Selina confronts Arthur about his crazy idea. Selina commands Arthur to throw the corpse away and apologize to Patrick. Blaming Zachariah for this fiasco, she forces him to go with Arthur.

Arthur and Zachariah bring the Mako shark up to the bank of an estuary. Arthur cuts the rope off the Mako shark's neck, discovering the deep pink scarring that it left behind. Arthur rolls the shark into the estuary. As Arthur watches the shark awkwardly sink to the ocean floor, he comes to understand that death is permanent and simultaneously realizes the cause of her death. Arthur throws the fishing rope in the trash bag and scours the beach for other garbage. Suddenly, the ocean breeze activates a sixth sense in Arthur, and he follows his intuition to the tide pools, where he finds the rare queen conch shell. He puts it to his ear and watches the ocean waves ebb and flow, but he hears the deep slow rumble of the entire underwater world.