Twelve-year-old Gap and her best friends, Jubes and Picca, are vovs who live in the Community of Zavaar, deep below the city of London. The humans above ground have no idea of the ancient civilization thriving beneath their city. Gap and her friends would tell you that's a good thing. They don't want any trouble from humans. But trouble is coming. When the annual field trip to the human-polluted River Fleet is cut short by an explosion, Gap and her friends set out to explore the Rock, where you should NEVER go unless you want your brains sucked out through your nose by monsters no one has lived to describe. That's what Gap's Uncle Biv says, anyway. In the Rock, Gap learns that the Community of Zavaar is in danger, but this is bigger than just Gap's world. The entire multiverse is at risk. Gap must take action, and Jubes and Picca will not let her do it alone, no matter how much she argues with them.You can't save the worlds alone.