The Obsidian Chamber (Special Agent Pendergast Series #16)

A TRAGIC DISAPPEARANCE
After a harrowing, otherworldly confrontation on the shores of Exmouth, Massachussetts, Special Agent A.X.L. Pendergast is missing, presumed dead.
A SHOCKING RETURN
Sick with grief, Pendergast's ward, Constance, retreats to her chambers beneath the family mansion at 891 Riverside Drive—only to be taken captive by a shadowy figure from the past.
AN INTERNATIONAL MANHUNT
Proctor, Pendergast's longtime bodyguard, springs to action, chasing Constance's kidnapper through cities, across oceans, and into wastelands unknown.
BUT IN A WORLD OF BLACK AND WHITE, NOTHING IS AS IT SEEMS
And by the time Proctor discovers the truth, a terrifying engine has stirred-and it may already be too late . . .