What they needed was an expert to go back to the Empty World and find the lost grown-ups. What they had was Christy. With the ever-faithful Trevor in tow, Christy defies her mother's wishes and ventures back to the Empty World. Her father and Detective Lockhart have been missing for months, and she's determined to bring them home safely. But trouble-maker Cory has his own reasons for wanting to go back, and he bullies Christy and Trevor into taking him along. The search takes them to a mysterious underground city, abandoned by an ancient race. Even if they find Mr. Walker and Detective Lockhart, will they be able to find their way back out again? And what of the secretive figure who seems to be following them? The city holds all the answers they need ... if they can find them. At the Portal's End is the third book in the Empty World Saga, a science fiction adventure series for kids aged 8-12. If your kids have blown through the Land of Stories, devoured the Keeper of the Lost Cities, or can't wait for the next Wings of Fire, make the complete Empty World Saga their next read. Grab At the Portal's End and solve the puzzle of the ancient aliens!