A lot has changed for Rayleigh Mann in the last few months.

On the previous All Hallow's Eve, Rayleigh was just a regular boy. Or he thought he was. Now, Rayleigh has embraced his monster heritage, passed all the tests to stay in Below London with the rest of monster society, and even saved his father - the Bogey Mann - from the notorious Illustrious Society.

But his adventures are far from over.

With the return of the Imposter and the Illustrious Three, Below London is on edge, waiting for the other shoe to drop. Since Rayleigh's own actions foiled the Illustrious Three's sinister plot last time, he's supposed to be staying far away from trouble. But as strange shadows start to reach out to him for help and clues begin to fall into place, Rayleigh and his new friends find themselves embroiled in a mysterious treasure hunt to prevent Below London from falling into chaos - and not the good kind this time.