Thomas the Tank Engine Sings Mamma Mia! is another upcoming Thomas & Friends crossover film to be created by 76859Thomas and LegoKyle14. It will appear on Google Drive or Dropbox in the near future.
On the Greek island of Kalokairi, 20-year-old bride-to-be Sophie Sheridan reveals to her bridesmaids that she has secretly invited three men to her wedding without telling her mother, Donna. They are the men that her mother's diary reveals could have been her father: Irish-American architect Sam Carmichael, Swedish adventurer and writer Bill Anderson, and British banker Harry Bright. She dreams of being given away by her father at her wedding, and believes that after she spends time with them she will know which is her father.
Sophie's mother Donna, who owns a villa, is ecstatic to reunite with her former Dynamos bandmates, wisecracking author Rosie Mulligan and wealthy multiple divorcée Tanya Chesham-Leigh, and reveals her bafflement at her daughter's desire to get married. Donna shows off the villa to Rosie and Tanya. The three men arrive and Sophie smuggles them to their room. She does not reveal that she believes one of them is her father, but does explain that she and not her mother sent the invitations. She begs them to hide so Donna will be surprised by the old friends of whom she "so often" favourably speaks. They overhear Donna working and swear not to reveal Sophie's secret.
Donna spies them and is dumbfounded to find herself facing former lovers, demanding they leave. She confides in Tanya and Rosie that she truly does not know which of the three fathered Sophie. Tanya and Rosie rally her spirits by getting her to dance with an all female ensemble of staff and islanders. Sophie finds the men aboard Bill's yacht, and they sail around Kalokairi, telling stories of Donna's carefree youth. Sophie plans to tell her fiancé Sky about her ploy, but loses her nerve. Sky and Sophie sing to each other, but Sky is abducted for his bachelor party.
At Sophie's bachelorette party, Donna, Tanya, and Rosie perform. When Sam, Bill, and Harry arrive, Sophie decides to talk with each of them alone. While her girlfriends dance with the men, Sophie learns from Bill that Donna received the money for her villa from his great-aunt Sofia. Sophie guesses she must be Sofia's namesake. She asks him to give her away and keep their secret until the wedding. Sophie's happiness is short-lived as Sam and Harry each pull her aside to tell her they are her father and will give her away. Sophie, overwhelmed by the consequences of raising the hopes of all three "fathers", faints.
In the morning, Rosie and Tanya assure Donna they will take care of the men. Bill and Harry intend to tell each other what they learned the previous night, but Rosie interrupts them. Donna confronts Sophie, believing Sophie wants the wedding stopped. Sophie says that all she wants is to avoid her mother's mistakes. Sam accosts Donna, concerned about Sophie getting married so young. Donna confronts him and they realize they still have feelings for each other. Tanya and young Pepper continue flirtations from the previous night. Sophie confesses to Sky and asks for his help. He reacts angrily to Sophie's deception and she turns to her mother for support. As Donna helps her daughter dress for the wedding, their rift is healed and Donna reminisces about Sophie's childhood. Donna admits her mother disowned her when she became pregnant. Sophie asks Donna to give her away. As the bridal party walks to the chapel, Sam intercepts Donna, who reveals the pain she felt over losing him.
Sophie and Donna walk down the aisle as the band plays. Donna tells Sophie and all gathered that her father could be any of the three men. Sam reveals that while he left Donna to get married, he did not go through with it, but returned to find Donna with another man. The men do not want paternity confirmed, agreeing to be one-third of a father for Sophie. She tells Sky they should postpone their wedding and travel the world. Sam proposes to Donna. She accepts and they are married. At the reception, Sam sings to Donna, Rosie makes a play for Bill and Harry openly admits he is gay. The couples proclaim their love. Sophie and Sky sail away.
- Sooty, Sweep, Soo, Little Cousin Scampi, Annoying Orange, Pear, Apple, Passion Fruit, Midget Apple, Marshmallow, Grapefruit, Grandpa Lemon, Nerville, Princess Knight, Choppy, Prince Frank, Zenda, Discord, Sunset Shimmer, Verity, Verity's Piplup, Sorrel, Sorrel's Lucario, Bill and Ben, Diamond Tiara, Silver Spoon, Sora, Riku, Kairi, Mickey Mouse, Pluto, Donald Duck, Goofy, Bugs Bunny, Daffy Duck, Dumbo, Timothy Q. Mouse, Jim Crow and his Brothers, the Mighty Morphin Power Rangers, The DigiDestined and their Digimon, Woody Woodpecker, Ttark, Alex, Marty, Melman, Gloria, Crysta, Batty Koda, Pips, The Beetle Boys, Tino Tonitini, Lor McQuarrie, Carver René Descartes, Tish Katsufrakis, Otis, Pip, Abby, Pig, Freddy, Peck, Duke, Lincoln and his sisters, The Powerpuff Girls (Blossom, Bubbles and Buttercup) and The Bakugan Battle Brawlers and their Bakugan are guest starring in this film.
- Dan Kuso will reveal that Sky is his Greek cousin.
- Pierce Brosnan who was the actor of Sam Carmichael in the real film, Mamma Mia! was also the guest starring narration of Thomas & Friends: The Great Discovery which they were both released in 2008 as well as Thomas & Friends: Season 12 first broadcast in the UK and Madagascar: Escape 2 Africa first released in theaters.
- Both Woody Woodpecker and Mamma Mia! were released by Universal.
- The storylines continues in Thomas the Tank Engine Sings Mamma Mia! Here We Go Again.