Some time after Nemo was reunited with his father Marlin, Dory is currently living with them. During a school lesson, Dory has a flashback where she realizes that she has a family. She decides to go to Morro Bay, accompanied by Marlin and Nemo.
The two are brought to California by Crush, where they are attacked by a squid that injures Nemo. Upset, Marlin chastises Dory for getting them into the mess. Shortly afterwards, Dory is taken by the staff of a Marine Life Institute, who place her in Quarantine and tag her. There, she meets an octopus named Hank, who wants to live in an aquarium and agrees to help Dory find her parents in exchange for her tag. During their quest, the two meet Dory's childhood friend Destiny, a whale shark, and Bailey, a beluga whale. Meanwhile, Marlin and Nemo, with help from two sea lions named Fluke and Rubber and a common loon named Becky, manage to get into the Institute.
Dory remembers how she was separated from her parents: she was pulled through an undertow current while searching for a shell to cheer up her mother. She travels through the pipe system and reunites with Marlin and Nemo, and they locate the other regal blue tangs, who explain that Dory's parents left the Institute years ago to search for her.
Hank retrieves Dory, but he is apprehended by the Institute employees, causing him to drop Dory into the drain, flushing her into the ocean. While wandering aimlessly, she follows a trail of shells to an empty home, where she reunites with her parents, Jenny and Charlie. They explain that they have spent years forming shell trails in the homes that it would lead her to them. The three then set off to rescue Marlin and Nemo, who are trapped in a truck taking aquatic life to Cleveland. With help from Hank, Destiny and Bailey, they hijack the truck and free those trapped inside, releasing them into the ocean.
Afterwards, Dory, reunited with her parents and newfound friends, returning to the reef with Marlin and Nemo.