As we start out the film, we are reintroduced to the characters from the first film. Sawyer (Nathan Gamble), the boy who was once instrumental in saving Winter, is now an integral employee at the Clearwater Marine Aquarium, and is training new volunteers at the aquarium. This is not the same aquarium we see from the first movie. This is now a larger, more modern, and well-funded aquarium.In the opening to the film, we are introduced to a new dolphin named Mandy. Clearwater Marine Aquarium (CMA) has rescued Mandy after Mandy was stranded near a beach and discovered by a little girl. Mandy has a bad sunburn and some respiratory problems from being stranded in the sun too long with her blowhole mostly exposed. Mandy is being rehabilitated at CMA.Winter has a friend at CMA named Savannah. Like Winter, Savannah cannot return to the ocean. Savannah is deaf and is quite old for a dolphin. She is expected to be at least 40 years old. It is alluded to that Savannah has some health issues and it appears by Winters erratic actions that she is concerned about her dolphin friend Savannah.On the human side of the film, Sawyer is approached by a professor (Carlos Gómez) from Boston about joining an elite Semester at Sea program for three months. Only one high school student per year is selected for this program. It comes with a full scholarship and his family is excited for him to have this opportunity. Sawyer is unsure whether he wants to go. He is concerned about leaving Winter for an extended period of time.When Sawyer returns the aquarium, Savannah has been found lying in the bottom of her tank dead. Her death happened very quickly, but does not come as a complete surprise because of her advanced age. All employees of CMA are very upset. However, the death is the hardest on Winter. Winter stops eating much and refuses her prosthetic tail. Her health starts to deteriorate for these reasons. Tests show she is under stress.An inspector (Charles Martin Smith) for the USDA comes to visit CMA and check on the animals. He gives Dr. Clay (Harry Connick Jr) a violation for keeping Winter in isolation and because of her deteriorating health. He issues as requirement that Dr. Clay matches Winter with another female dolphin within 30 days. In the meantime, Winter continues to be very unhappy. When Sawyer attempts to get her out of the tank for a new cast of her tail Winter becomes aggressive and knocks into Sawyer, injuring his wrist and giving him a bruise on his face. Dr. Clay orders that Sawyer has to take a break from swimming with Winter.Everyone at CMA stakes their hopes on Winter being paired together with Mandy in order to satisfy the USDA and improve Winter's health. However, Mandy has improved greatly and has a clean bill of health. Dr. Clay says Mandy can be returned to the ocean. Dr. Clay's daughter Hazel (Cozi Kuehlsdorff) is unhappy because she doesn't want Winter to be transferred. She wants Mandy to stay with Winter for a short period of time to keep her from being transferred, even though she can return to the ocean. Dr. Clay makes clear that the goal of CMA is Rescue, Rehabilitate, Release. They cannot morally keep Mandy when she could return to the ocean. He has to make the call to return Mandy to the ocean, even though it becomes clear that doing so will cause Winter to be transferred to a marine park in Texas. Mandy is returned to the ocean and Hazel steps up to take a key role in her return.Hazel and Sawyer break Dr. Clay's rule and swim with Winter. The dolphin seems improved. She is no longer aggressive. Sawyer and Hazel think she is improving. Dr. Clay says she will be transferred regardless.Sawyer's mom (Ashley Judd) throws a party for him to congratulate him for being chosen for the Semester at Sea. She wants to push him towards a decision. Sawyer is still too upset about Winter. During the party, Dr. Clay gets a call. A juvenile female dolphin has been rescued and is headed to the hospital. Everyone leaves the party and rushes to CMA to prepare for the arriving dolphin. Dr. Clay, Sawyer, Hazel and the trainers know this is the hope to keep Winter at CMA. They name the tiny dolphin Hope.As a humorous side note to the main story, the team also rescues a sea turtle who was stuck on some fishing line. Pesky pelican Rufus seems obsessed with this sea turtle named Mavis. Rufus follows the sea turtle everywhere, even to a hospital for humans where it gets a CT Scan. When Mavis is released into the ocean, Rufus flies over it as it swims into the sea.Dr. Clay got an extension to keep Winter from being transferred with the addition of Hope at CMA. The first time they put the two dolphins together, Hope's echolocation senses that Winter has no tail and moves differently. This makes Hope feels threatened and swim aggressively. Winter follows suit. Dr. McCarthy designed yet another prosthetic tail for Winter that looks even more realistic than her previous tail. In their second meeting, Winter wears the tail. The two dolphins get along. Everyone rejoices that Winter will get to stay at CMA now that she has a friend and will no longer be isolated and lonely.With Winter's improvement, Sawyer decides to do Semester at Sea. Hazel releases balloons for him as he leaves and tells him how much she will miss him. As the credits roll, we yet again see interactions between Winter and real people who use prosthetics. Surfer Bethany Hamilton makes a cameo in the movie as a supporter of Winter.