Gregor and the Curse of the Warmbloods

Gregor turns to the Prophecy of Blood when a plague begins spreading through the Underland. The prophecy requires him and his younger sister, Boots, to return below New York, this time accompanied by their mother. When the disease strikes someone in Gregor's own family, the mission becomes personal. He must understand his role in the prophecy and help stop a form of biological warfare before the warm-blooded creatures of the Underland are destroyed.