Mario and The Luigi Files is a game by Nintendo. It is the first part of the Mario and Luigi: Early Years Series.
Prolouge: Mario The Plumber
Mario is at a house plumbing when he finds a mysterious pipe. It is green and big. He decides to jump inside. When he is inside, there is a white mushroom man. He looks around and realizes he will have to stay there for the rest of his life.
Chapter 1: The Lost Brother
5 years later. Mario and Toad are getting ready for his wedding with Peach. Toadbert is playing the out-of-tune piano. When Peach is walking, Toadsworth comes in panicking. He yells to everyone that a giant 50-foot monster is attacking the kingdom! Mario runs outside and sees a yellow turtle guy. He reads a book that says what everything is in the Mushroom Kingdom. The first page you see says TOAD. The second says YOSHI. The third says BOWSER. He studies it carefully and the wind flips the pages and it says MARIO'S BROTHER LUIGI. You then play the first levels running to E. Gadd Lab.
Chapter 2: The Scientist
Prof. E. Gadd is in his lab, creating the Polterguster 3000 and F.L.U.D.D. He suddenly realizes he needs a potion from the Mushroom Kingdom Sewers. You run everywhere as Gadd finding weird potions and swimming in the sewer.
Chapter 3: Luigi The Plumber
It goes back to 5 years ago where Mario and Luigi are plumbing in different areas. The caller who's pipe got Mario calls Luigi after he "disappeared." He too gets sucked down the pipe, except ends up in Bowser's Castle, which was originally called Luigi's Castle for 5 years. Many goombas served Luigi. One of the goombas wrote the book that Mario was reading. Luigi has to go around his castle to tell his minions some stuff.
Chapter 4: Back Then
Mario finds Gadd in his lab with a strange potion. Mario asks him about Luigi. Gadd drinks the potion, which makes him 1,000 times smarter. He says that Luigi is trapped in Bowser's Castle and is his long lost brother who he forgot after he went down the drain in Italy. Mario travels through Nightsky Mushroom Kingdom, AKA The Dark Side.
Chapter 5: The Wedding
Peach is looking for Mario in Toad Town and is also trying to find Toadsworth, who put a tracker on Mario at all times so she can see.
Chapter 6: The First Attack of Goombas
Bowser unleashes an evil army of brainwashed goombas! However, the Mushroom Kingdom brings out the Koopa Troop! Play as a Red-Shell Koopa Trooper on your way to defeat Bowser!
Chapter 7: Bowser's Brainwashed Koopa Troop
Bowser brainwashes the Koopa Troopers and renames them Koopa Troopas. Luigi is in a cage and remembers his brother Mario. He hopes that Mario will save him. Mario must go farther into the Dark Side: Lakithunder's Dark Skies!
Chapter 8: The Darker Side
Bowser's relative Morton Koopa Sr. calls in angrily. Will Bowser go to defeat King Koopa? Trivia: One of the Koopalings (Not the Fantendo Koopalings) is named after Morton Koopa Sr. (Morton Koopa Jr.)
Chapter 9: The Wrong Place
Mario finds Bowser's Castle. Too bad Bowser is in King Koopa Kastle! Can Mario get there?
Chapter 10: King Koopa Kastle
The first chapter where you have a player choice. You can be Mario or Luigi. Luigi can call his Goomba Army if you get a Powershroom.
Chapter 11: THAT Wasn't The End?!
Mario wasn't finished on his adventure?! Well, he WAS. These are Bonus Levels. You can play as any character from the game that is playable. You can also unlock Goomba, Warrior Goomba, Toadbert, and Mr. L.
The Double Wedding
The last scene. Complete every chapter and it will have a wedding with Peach and Daisy walking together, Toadbert and Toadette playing the piano, and Mario and Luigi standing. When Peach has fully walked down the aisle, Toad has a camera and you see a flash and then it says NOW on the screen. Mario is holding a picture in the present. Peach says, "And that's the story of how we got married."