In Sam London's third adventure with the Department of Mythical Wildlife, the boy who saw the gryphon will face his greatest fear. Following the heartbreaking conclusion of his second case, Sam has spent his days searching for the swan maiden. Driven by his belief the maiden is still alive, he sets out with Dr. Vance Vantana and Tashi on a forbidden quest to reunite his family.

But the journey is long and treacherous and will lead them through the lair of the Mongolian Death Worm—a terrifying creature that has broken the Gryphon's Law and is attacking anyone who dares to cross its path. And if this wasn't enough, an old enemy from Vance's past returns to exact a revenge that will doom all of humankind.

With the future of his family and the fate of the world at stake, Sam must make an impossible choice that will change the course of his life and those he loves forever. Can Sam right a wrong or will Gaia, itself, decide to fight back?