The Discovery of Multiplus Minus is an unofficial name for a story by unknown authors. In addition to being a story in itself, it serves as a framing sequence for the stories Donald Ducks Out, Mickey Mouse in Spaceball, and Minnie Mouse in Lost in the Space Lab. It features Donald Duck, Huey, Dewey, and Louie Duck, Scrooge McDuck, Ludwig Von Drake, Daisy Duck, Mickey Mouse, Minnie Mouse, Goofy, Pluto, Jiminy Cricket, Dumbo, and, in their debut, the Space Robots.
After designing a rocket with his nephews, Donald Duck proposes a new money-making plan to Scrooge McDuck: space mining. And, what's more, he knows the perfect planet for it: Multiplus Minus, a yellow-tinted world just beyond Mars. Scrooge loves the idea, and, true to form, sends Donald and his nephews to the planet to work as his new space miners. Unfortunately for the old miser, the plan ends up costing him two million dollars.
Scrooge's fortune soon changes, though - he begins pulling in large sums from the project, making, at one point, ten million dollars in one day. He soon enlists the help of Ludwig Von Drake to help him add it all. Meanwhile, Mickey, Minnie, and Pluto travel to space in their own ship and admire the stars, while Dumbo makes his way into orbit and puts his famous powers of flight to use by traversing the galaxy with nary a spacecraft. Back on Earth, Jiminy Cricket counts the stars using his telescope, while Goofy, apparently unconcerned with the spacefaring adventures of his friends, attempts to balance various cups and saucers on his nose.
After an incident involving disco that prompts Donald to move to Multiplus Minus permanently, Mickey and his group travel to the planet Pluto, where they discover that the Sun, from that distance, looks like the rest of the stars do from Earth. Donald proposes a brand-new rocket engine to Scrooge, which he claims can travel five times faster than the one that the fantasticatrillionaire has been using, while Pluto attempts to lose weight after eating too much dog food while feeling weightless in space.
Goofy joins the gang in space, and, after a game of Spaceball on Multiplus Minus, Daisy, back on Earth, receives a present from Donald, sent from space. She sends Donald and the nephews cupcakes in return, and they divide them between each other.
Donald attempts to convince Scrooge to make him and the boys equal partners in the enterprise, but Scrooge characteristically refuses. Mickey, Minnie, and Pluto go jogging, and Pluto loses weight.
Minnie becomes lost in the Space Lab, but manages to find her way out, and so ends the group's adventures in outer space.
- Donald Duck manages to design a working rocket, which is approximately 9 feet tall
- Multiplus Minus, a planet in the Solar System, is very close to mars, and it only takes three days longer to get there from Earth than it takes to reach Mars.
- Jiminy Cricket feels that the biggest number in the universe must be the number of stars plus the number of bugs.
- Multiplus Minus is a yellow planet with white rocks strewn about its surface, and valuable black rocks located beneath.
- The Space Mining Rocket uses four tons of fuel to get to Multiplus Minus, and three tons to get back.
- Donald and his nephews use shovels to dig up 'space rocks' from Multiplus Minus. On their first day there, they managed to dig up at least nine pounds of rocks.
- Donald's space mining plan initially costs Scrooge two million dollars, but it later makes him at least ten million dollars per day.
- Flying in his saucer, it takes Mickey five hours to break out of the Earth's atmosphere, but only two hours to re-enter.
- On Earth, Pluto ate two bowls of food per day, but in space, feeling weightless, he ate six bowls per day instead.
- Before taking up jogging, Pluto weighed twenty-four pounds, but after, he weighed twelve.
- Donald moves to Multiplus Minus in Donald Ducks Out (1980).
- Mickey hosts a game of Spaceball on Multiplus Minus in Mickey Mouse in Spaceball (1980).
- Following her adventures on Multiplus Minus, Minnie became lost in the Space Lab in Minnie Mouse in the Space Lab (1980).