It is nice to see someone reading one of my favorite books!
In the first chapter, we are told that the professor insisted on telling his story to the Western American Explorers' Club in San Francisco, specifically in the auditorium of the Club. The professor's insistence leads to some hurt feelings because the person who rescued him, Captain John Simon, felt that since he had gone to such trouble to rescue the professor, he should hear the story first. Similarly, the ship's doctor and the cook had gone to a great deal of trouble for the professor after he was rescued. So they were disappointed, too. The book says, They were all three most disappointed (10).
Because the professor insists upon waiting until he gets to San Francisco and preparations are made for this great event, peoples' curiosity gets built up and the captain, the doctor, and the cook try to trick him into revealing his story. They try to get him drunk, give him drugs, and still, all the professor will reveal is his name.
I hope you are enjoying the book. Good luck to you.