When fifth grader Penny Lowry and her classmates get invited to go to New York City for a weekend hosted by Billy J. Plumberry, the famous author her school is named for, Penny finds a lot to worry about. After all, isn't the city full of aggressive bike messengers ready to run kids over? And what if she gets stuck in an elevator for life? Not to mention all the pianos falling out of windows everywhere!

On the other hand, what if it might actually be fun to explore an exciting new place with some of her best friends?

When it soon becomes clear Billy J. Plumberry has a few surprises in store, can Penny find a way to face her fears--and her worries--in the biggest, bustling-est place she's ever been?