Charlie and the Great Glass Elevator is the sequel to Roald Dahl's classic children's book Charlie and the Chocolate Factory.
The book begins where Charlie and the Chocolate Factory ends: Willy Wonka has just given Charlie the ownership of his chocolate factory, and they crash through the roof of Charlie's house with a flying elevator to inform his family of the good news. Charlie's grandparents (except Grandpa Joe who had already gotten out of the bed) are nervous about going inside the travelling elevator, and after twenty years in bed, they refuse to get up. The bed is thus pushed into the elevator, which then takes off. At a critical moment during the return trip to the factory, a panicking Josephine grabs Wonka away from the controls, which results in the elevator, along with its occupants, being sent into an Earth orbit. The elevator circles the planet until Wonka sees the chance to link it with the newly-launched Space hotel, a creation of the United States government.
In the White House, President of the United States Lancelot R. Gilligrass, together with Vice President Elvira Tibbs (who was once Gilligrass's nanny) and the entire U.S. Cabinet see a mysterious object (the glass elevator) dock with the Space Hotel. They fear it contains hostile agents of a foreign or extraterrestrial government who seek to blow up the Space Hotel. The space shuttle containing the hotel staff and three astronauts approaches the Space Hotel and the shuttle's crew prepares for the worst. On the Hotel, Wonka and the others hear the President address them across a radio link as Martians, and Wonka proceeds to tease Gilligrass with nonsense words and grotesque poetry. In the midst of this, the hotel's elevators open, revealing five gigantic, brown-green, boneless creatures shaped something like eggs with eyes, which change shape, each forming the letters of the word SCRAM. Recognising the danger, Wonka motions everybody to get out of the Space Hotel quickly.
Those shape-changers, Wonka tells the e others, are predatory extraterrestrials called Vermicious Knids that have infested the Space Hotel. Since they can't reach Earth's surface to prey on its natives because they burn up in the atmosphere as shooting stars, the Knids are waiting in the Space Hotel for the new arrivals. Meanwhile the shuttle docks with the Space Hotel and the staff and astronauts go aboard. The Knids reappear and devour some of the humans, but most of them escape back to the spacecraft. Capable of flying in the vacuum of space at improbable speeds, they pursue the survivors but are unable to board the space shuttle. Instead, they dive-bomb the shuttle's engines and hull, destroying the rockets as well as the cameras and radio antenna. Without its engines, the shuttle is unable to escape the Knids by breaking orbit and returning to Earth.
Seeing all this from the relative safety of the Great Glass Elevator (which is "Knid-proof" – one Knid bruised itself badly on the glass and has been chasing the Elevator ever since), Charlie suggests that he and his companions use the Elevator to tow the shuttle back to Earth. In agreement, Wonka pilots the Elevator into range, whereupon Charlie's Grandpa Joe connects the two vessels by means of a steel cord. The Knids change into living segments of a towing line, with which they intend to drag the two spacecraft away, while the bruised Knid wraps his body around the Elevator to provide an anchor for this operation. Willy Wonka activates the Elevator's retro-rockets and plunges to Earth, taking the shuttle and Knids, all of whom burn up due to friction with the atmosphere during re-entry. At the right moment Wonka releases the shuttle, which floats safely home. The Elevator then crashes into the chocolate factory, ending its flight in the Chocolate room.
Since Charlie was presented the factory as a gift by Wonka, he wants his family to help him run it. Georgina, George and Josephine still refuse to move out of their bed. Wonka proposes a pill he invented, Wonka-Vite, to make them young again. (He says that it is too valuable to waste on himself, which is why he needed an heir in the first place.) The three bedridden recipients get greedy and take much more than they need to. Instead of becoming a mere twenty years younger, the three grandparents lose eighty years, making George one year old, Josephine three months, and Georgina absent altogether, having become "minus two" (she was seventy-eight). Charlie and Wonka journey in the Great Glass Elevator to Minusland – a realm that Wonka discovered when his earlier attempts to create Wonka-Vite turned all the Oompa-Loompas he tested it on to become Minuses as the formula was too strong – to get Georgina back with Vita-Wonk, a sprayable compound that makes people older. Minusland is a dark, gloomy region far beneath the surface of the Earth, filled up entirely with fog, and inhabited only by the invisible and highly dangerous Gnoolies, creatures which, with a single bite, turn their victims into more Gnoolies (Wonka states that the process, a form of long division, takes a long time and is very painful). After administering an even worse overdose of Vita-Wonk to Grandma Georgina, they return to the upper world.
There, Georgina has become 358 years old. Her memory entails a lot of history, beginning with the Pilgrim voyage in the ship "Mayflower" (which Wonka and the Buckets use to pinpoint her exact age) and ending in the present moment, spanning over many wars and truces in between. Using a more cautious dose of Wonka-Vite, her companions subtract much of this age from her, leaving her at seventy-eight as she was before. During the process of becoming younger, she shouts several sentences, all having to do with American History, including: "We've beaten them! Yorktown's Surrendered! We've kicked them out, those dirty British!", "Gettysburg! General Lee is on the run!", "He's dead, he's dead, he's dead!", "Lincoln! There goes the train..." Charlie and Mr. Wonka administer enough Vita-Wonk to recall Josephine and George to their original age.
The grandparents are still incensed with Wonka's adventurous nature. They refuse, as before, to come out of bed. Then mysterious visitors arrive in a helicopter. The Oompa-Loompas give Wonka a letter from President Gilligrass, congratulating the occupants of the Great Glass Elevator on saving the lives of the shuttle astronauts and hotel staff and inviting them as the guests of honor to a White House dinner. The grandparents don't want to be left out, so they leap out of bed and join Charlie, Grandpa Joe, Wonka, and Charlie's parents to enter the helicopter sent to pick them up.