Willy Wonka takes an exciting, roundabout way back to the factory with Charlie Bucket and his family, and succeeds after several failures to get Charlie's grandparents out of bed. The story begins exactly where Charlie and the Chocolate Factory left off. Charlie's parents and grandparents, along with their bed, have been loaded into Willy Wonka's great glass elevator. Now Willy Wonka informs them that they must go up before they can go down, so that they can be going fast enough to punch a second hole in the roof in the top of the factory (because who would think of using the first hole they created when they can create a second hole; as Wonka tells them, any mouse knows that two holes is better than one). Charlie's three bedridden grandparents, especially the cranky old Georgina, are quite alarmed and distrustful of the rather odd candy-maker, and prevent him from pressing the right buttons at the right time. As a result, the elevator goes into orbit around the earth.
Once in orbit, they discover they are remarkably close to a space hotel build by the American government, which of yet is unmanned. They decide the go take a look as the first humans to go aboard. Meanwhile, a spacecraft with all the hotel's astronauts and workers is approaching and is in communication with Houston and Washington DC. Pretty soon, the entire world is staring at the glass elevator and its passengers via television signal beamed down from the spacecraft, and Washington is freaking out. The head of the army keeps asking to blow them up, but the president's nanny keeps everything under control.
Up in space, Willy Wonka, with the help of Charlie and his grandpa Joe, guides the spacecraft onto the ship. Once on the spacecraft, the US government first tries to threaten them into giving their names. When Willy Wonka frightens them by bluffing in gibberish, the government invites the hotel's first guests, now thought to be visitors from Mars or Venus, to the White House. Wonka also scares the government into thinking there are squishy, dangerous aliens up there.
As Wonka and his crew then find out, there actually are squishy aliens up there - dangerous, egg-shaped Vermicious Knids, who can stretch themselves into any desired shapes. They are already in the hotel and decide to take control of the hotel elevators, which open, and the Knids twist themselves into five letters: S-C-R-A-M. Wonka and company scram into their knid-proof elevator. The government's spacecraft, unaware of the danger, docks and loses 2 dozen crew members to the knids before escaping.
Wonka, Charlie, and Grandpa Joe have been directing the elevator in orbit in double time away from a knid that is frightening Grandma Georgina, but which they can't lose. They see the knids coming out of the hotel to attack the government spacecraft, whose rockets have failed, so they hook up with the spacecraft and pull it into Earth's atmosphere, which is dangerous to the knids when entered at high speeds, and unhooks when they know the spacecraft will be able to use its parachutes to return safely to the ground.
Back at the factory, Wonka wants Grandma Josephine, Grandpa George, and Grandma Georgina out of bed and helping with the factory. They haven't been out in 20 years and stubbornly refuse to get out. Wonka tries tempting them with pills (dubbed Wonka-Vite) that each have the power to make a person twenty years younger. The three in bed start grabbing and fighting over them, and take four each. Grandpa George and Grandma Josephine end up as babies. Grandma Georgina was only 78, so Wonka and Charlie must go into Minusland (where dangerous invisible creatures lurk) to rescue her. Wonka uses an aging spray he invented (Vita-Wonk) to bring her back - a little too much. At 358 years old, it takes 14 Wonka-Vites to bring her back to her original age. They then use Vita-Wonk to bring Grandpa George and Grandma Josephine back to their original ages.
All three still refuse to get out of bed. This changes when Willy Wonka receives a letter from the US Government, which tracked the elevator back to the factory. They are invited as their own heroic selves (and not as aliens from Mars or Venus) to Washington DC as honored guests for saving the government craft. This is an invitation no one can or will refuse - even if the bed that's holding them can't fit into a government helicopter.
Best part of story, including ending:
Even though the book (like some of his other stories) is totally unrealistic, Roald Dahl keeps the tone such that the reader can suspend disbelief, yet simultaneously remain entirely clear on what is or isn't supposed to be unrealistic. The characters' attitudes are one of the most important "real" things in the book, and the reader will (hopefully) understand after meeting Wonka in this book or in Charlie and the Chocolate Factory that sometimes a little bit of craziness can be good for you.
Best scene in story:
After Charlie and Willy Wonka rescue Grandma Josephine from Minusland, Georgina's face is described like a prune, and she has so many years in her that she can't clearly remember it all. She does remember the Mayflower, though. As she begins to grow younger again, she remembers several important events in American history, such as the revolutionary war and the civil war, which flash by and then disappear. This was the most memorable part of the book for me.
Opinion about the main character:
Charlie is in theory the protagonist, but Willy Wonka really does more to keep things moving forward; Charlie is more like an observer and helper discovering his new factory. He does prompt Willy Wonka when they need to go back into earth's atmosphere, though - rather important with all the Knids on their tail. It's also interesting to hear later why Mr. Wonka won't use the Wonka-Vites on himself: He considers them much to valuable. And yet he goes through many more of them on Charlie's grandparents.