From #1 best-selling author Rick Riordan and award-winning author Mark Oshiro comes a new adventure featuring two of the most popular characters from the world of Percy Jackson and the Olympians.

It's been three months since demigod boyfriends Nico di Angelo and Will Solace returned from Tartarus, and there hasn't been a single quest for them in all that time. So, when Nico's half sister Hazel asks them to come to Camp Jupiter to help with an 'issue', Nico shadow-jumps at the chance to do something.

What Hazel didn't tell the boys is that she's providing a haven for a group of monsters who've escaped the Underworld! Apparently, during Nico and Will's trip to the Underworld, they showed the monsters that they don't have to be evil - that the monsters have options.

But then the monsters start disappearing from the camp and it's clear a dark force is at work - and Nico, Will and Hazel are shocked to find that they're connected to it . . .