Jeremy Fink: The Flea Market

In chapter 4, Jeremy and Lizzy try to find the four keys at a huge flea market in New York City. I thought they would find at least one of the keys, because there were so many vendors who had boxes of old keys to sell. I felt nervous when they finally found a key that fit into a hole. Would it be the right key? Bad news. The key would not turn in the lock. Lizzy did not give up. She said, "That brings us to the next item on my chart. The one I hoped we wouldn't have to get to." What will happen next? What do you think Plan F is?