As the film unfolds, we reconnect with familiar faces from its predecessor. Sawyer (Nathan Gamble), who played a vital role in rescuing Winter, is now an essential part of the Clearwater Marine Aquarium, where he trains new volunteers in a significantly expanded and modernized facility compared to the first film.
At the beginning of the narrative, we meet a new dolphin named Mandy, rescued by the Clearwater Marine Aquarium (CMA) after being found stranded on the beach by a young girl. Unfortunately, Mandy suffers from severe sunburn and respiratory issues caused by her exposure to the sun. She is now undergoing rehabilitation at CMA.
Savannah, another dolphin at the aquarium, shares a special bond with Winter. Unlike Winter, Savannah cannot return to the wild and is in the twilight of her life, estimated to be around 40 years old. As the story progresses, Winter's concern for her friend Savannah becomes increasingly apparent, highlighting their deep connection.
On the human side of the story, Sawyer is approached by a professor (Carlos Gómez) from Boston with an incredible opportunity to join an elite Semester at Sea program, which lasts three months and is limited to just one high school student each year. His family is excited about this chance, but Sawyer hesitates, unsure about leaving Winter behind.
An unexpected blow comes when Savannah is found dead in her tank, a loss that the staff at CMA feels acutely, especially Winter, who spirals into despair, refusing to eat or accept her prosthetic tail. Sawyer witnesses Winter experiencing distressful behavior and faces an injury himself while trying to comfort her—proving just how fragile their relationship has become.
In a turn of events, an inspector from the USDA (Charles Martin Smith) issues a violation to Dr. Clay (Harry Connick Jr) for keeping Winter isolated, requiring him to pair her with another female dolphin within a month. The hope is pinned on Mandy, who restores her health and, despite her rehabilitation success, is poised for release into the ocean, which leaves the fate of Winter in jeopardy.
Hazel (Cozi Zuehlsdorff), Dr. Clay's daughter, plays a critical role as she stands against her father's decision to return Mandy to the ocean. Her desire for the dolphins to remain together contrasts with the mission of CMA—to rescue, rehabilitate, and ultimately release when possible.
In a twist, Sawyer's mother (Ashley Judd) throws a party to celebrate his nomination, hoping to encourage him to choose the program. However, a call interrupts the celebration—a juvenile female dolphin named Hope has been rescued, sparking urgent efforts from Dr. Clay and the team to prepare for her arrival at CMA.
As a subplot, the team also rescues a sea turtle tangled in fishing lines, leading to a humorous distraction from the main narrative involving a curious pelican named Rufus who forms an unexpected bond with the turtle.
With the arrival of Hope, Winter is given a new lease on life. A prosthetic tail designed by Dr. McCarthy allows Winter to swim alongside Hope, reintegrating her into social settings and ensuring she will not be alone any longer.
Eventually, empowered by Winter's renewed spirit, Sawyer makes the decision to participate in the Semester at Sea program. As he departs, Hazel releases balloons, signifying the bittersweet nature of their goodbye. The credits roll, emphasizing the enduring connection between Winter and those who have undergone similar struggles, with a cameo appearance from surfer Bethany Hamilton, who stands in solidarity with Winter’s journey.
