The Somebodies by N. E. Bode

There is a city beneath New York City, one made by and for Anybodies. There you can find Bing Chubb's Ballpark, Willy Fattler's ever–changing Underground Hotel, and a castle whose spire sticks up into the dirt–filled sky...dangerously close to the rear ends of unsuspecting picnic–goers in Central Park. It's an extraordinary place, but it is in danger of becoming ordinary because of the nefarious Blue Queen. Somebody has to stop her, and if anybody is going to, nobody is better than everybody's favorite Anybody. In her third quirky adventure, Fern takes on the biggest, baddest, bluest opponent ever. Yikes!