From the introduction:
Headquarters. Hideouts. Lairs. Labs. Be they caves, mansions, space stations, or extra dimensional hidey holes, bases of operation have long been a staple of super-hero stories. The best such places were as much characters as the heroes and villains of the tale, taking on a personality, style, and feel of their own. A hideout spoke volumes about its inhabitants; from the trophies kept there to the location of the hideout, important facets of the owner could be discerned. All in all, headquarters are much more than places to simply hang your cape and mask.
This book contains additional rules for new headquarters features, building superpowers into headquarters, and a number of example headquarters complete with their inhabitants. While it serves as a companion piece to Headquarters and Hideouts 1 the first book is not strictly required, though very useful. Headquarters and Hideouts 1 is not required to use this book, but there are many references to headquarters features and rules with in it.