The Isle of Blood — Rick Yancey

When Dr. Warthrop goes hunting the "Holy Grail of Monstrumology" with his eager new assistant, Arkwright, he leaves Will Henry in New York. Finally, Will can enjoy something that always seemed out of reach: a normal life with a real family. But part of Will can't let go of Dr. Warthrop, and when Arkwright returns claiming that the doctor is dead, Will is devastated -- and not convinced.

Determined to discover the truth, Will travels to London, knowing that if he succeeds, he will be plunging into depths of horror worse than anything he has experienced so far. His journey will take him to Socotra, the Isle of Blood, where human beings are used to make nests and blood rains from the sky -- and will put Will Henry's loyalty to the ultimate test.