Sophie Sheridan (Amanda Seyfried) is in the midst of organizing the grand reopening of her late mother Donna's (Meryl Streep) hotel, a year after her passing. She feels a profound sense of sadness as two of her fathers, Harry (Colin Firth) and Bill (Stellan Skarsgård), are unable to attend. Furthermore, her marriage to Sky (Dominic Cooper) faces strain as he is working in New York, complicating her efforts to celebrate her mother's legacy.
Flashing back to 1979, a young Donna is preparing to explore the world while feeling frustrated that her mother, [Ruby](./actor/cher), is absent from her graduation. Alongside her best friends from college, Tanya ([Christine Baranski]) and Rosie ([Julie Walters]), they proudly call themselves the "Dynamos." During her time in Paris, Donna meets and spends the night with Harry, who admits he's a virgin. Unfortunately, she misses her boat to Kalokairi, Greece, but her journey takes a turn when Bill offers her a ride. Together, they help a stranded fisherman, emphasizing Donna's adventurous spirit. Unknown to her, Harry has followed her to Greece, but he arrives too late and watches helplessly as her boat departs.
In the present day, Tanya and Rosie arrive to lend their support to Sophie during the hotel reopening, revealing that Rosie and Bill have parted ways. Shortly after, Sophie visits Sam ([Pierce Brosnan]), who is still mourning Donna's death.
Back in the past, Donna arrives on the island to explore her farmhouse but is interrupted by a sudden storm that leads her to a frightened horse in the basement. Seeking help, she encounters a young Sam riding his motorcycle, who comes to her aid, setting the stage for a romantic connection.
Returning to the present, a storm disrupts the reopening festivities and hampers media coverage. Meanwhile, young Donna and Sam are swept up in a passionate whirlwind romance. She confides in him her desire to stay on the island and share a life together. However, when she discovers a picture of Sam's fiancée, heartbreak drives her to send him away.
In the present, Sam reassures Sophie of her importance to her mother. At the same time, Harry abandons a business deal in Tokyo to be with Sophie, and Bill, motivated by the same sentiment, also seeks to support her. The two fathers meet at the docks, only to find that there are no available boats. Fortunately, Bill encounters a fisherman named Alexio ([Gerard Monaco]), securing passage for himself, Harry, and the newly arrived Sky. In an unexpected twist, Bill decides to invite the entire fishing village to join Sophie's celebration.
Back in the past, a heartbroken Donna channels her sorrow into music alongside Tanya and Rosie. Bill returns, rekindling their romance while Rosie harbors feelings for him, leading to a complicated dynamic. Meanwhile, Sam returns after ending his engagement for Donna but is devastated to find her with another man and leaves the island yet again. Donna soon discovers she is pregnant but remains uncertain about which of her three recent lovers is the father.
In the present, as the guests arrive for the party, Sophie is joyfully reunited with her two fathers and Sky. She shares her pregnancy news with Sky, feeling a deep connection to her mother's struggles. Bill and Rosie find solace in their shared grief for Donna. Unexpectedly, Sophie's estranged grandmother, Ruby, shows up, seeking to forge a new relationship with Sophie after being tracked down by Sky.
Sophie honors her mother by performing a song with Tanya and Rosie, receiving heartfelt praise from Ruby afterward. It is revealed that the hotel manager, Fernando, is Ruby's former lover, leading to a triumphant reunion.
Fast forward nine months later, Sophie's baby boy is welcomed for his christening amidst the warmth of family. As the ceremony unfolds, Tanya flirts with Fernando's brother, and the joyous occasion culminates with the spirit of Donna watching over her daughter. Ultimately, all characters, including Donna and the younger cast, unite in a spirited rendition of "Super Trouper" during a grand celebration at Hotel Bella Donna.
