The summary is based on the story "21 balloons" by William Pène du Bois
Professor Sherman was rescued when he was floating in the ocean with 20 balloons. Then he came back to his hometown and gave a speech about his journey around the world in fourty days.
Back to the August when the professor started working in his hot air balloon. He prepared everything carefully to make sure the trip will go smothly. Then, he started the trip, but unluckily, the balloon collapse and he crashed on an island.
Professor Sherman was awaked by a man- Mr.F. HHe guided the professor to diamonds mine and introduced him about the volcanic island- Krakatoa.
The next day on the island came, the professor got to know about the history of Krakatoa and got to know about their gourmet government.
Continue on the professor journey to know more about Krakatoa, he followed Mr.F to a house which is The Moroccan House of Marvels.
Mr.F showed Professor Sherman every invention in Mr.M house. After that, the professor became more interesting about the island.