At the request of Mr. F, the Professor gives a talk to a gathering of all the citizens of Krakatoa about San Francisco. While he is speaking, the land begins to shake even more ominously than usual, and the decision is made to evacuate. Everyone runs to their preasssigned chores and gathers at the balloon platform. The Professor is the last to arrive, and is helped onto the platform just as the balloon takes off.
After being stranded for seventeen hours in a vacuum directly over the volcano, the balloon is safely on its way. The passengers watch sadly as huge explosions demolish Krakatoa. Food is carefully rationed as the platform travels over the Indian Ocean, and when the land of India is reached, all the families but one parachute down. The Professor alone has no parachute, and the F family has volunteered to remain on the platform with him. The balloon continues over Europe, and in Belgium the F family finally leaves the Professor. The Professor struggles to navigate the unwieldy platform over the British Isles, and when he reaches the Atlantic, he crashes it into the sea. He is rescued by the S.S. Cunningham.
The scene shifts back to the beginning of the story, where the Professor is speaking about his adventures to the Western American Explorers' Club in San Francisco. When asked what he will do with his life now, he responds that he will sell the diamond cuff links given to him by Mr. F, and use the money to buy a balloon, on which he will spend a full year living in the air as he had originally planned (Chapter 10).