 What is the goal of the story that Simon tells Mr. Oyster?
It's my contention that within a century or so man will have solved the problems of immortality and eternal youth, and it's also my suspicion that he will eventually be able to travel in time. Simon seemed incapable of carrying the ball this morning, so Betty said, "But ... Mr. Oyster, if the future has developed time travel why don't we ever meet such travelers?" Mr. Oyster returned his glasses to their perch, bug-eyed Simon, but then nodded. Simon said, "You want to hire me to find a time traveler and in some manner or other—any manner will do—exhort from him the secret of eternal life and youth, which you figure the future will have discovered.
 He wanted to explain why the trip would not be successful if he went to Germany.
 Simon wanted to show that he had spent a lot of time thinking about encounters with time travelers.  He wanted to explain why the trip would not be successful if he went to Germany.  He wanted to mock his prospective client for his ideas about time travel.  He wanted to prove that Oktoberfest was the wrong place to look for time travelers.