The replacement - Brenna Yovanoff

Mackie Doyle is a replacement - a fairy child left in the crib of a human baby sixteen years ago, to replace the baby when it was stolen away by the fey.

So though he lives in the small town of Gentry, Mackie's real home is the fey world of tunnels and black, murky water, a world of living dead girls ruled by a little tattooed princess. Now, because his fey blood gives him fatal allergies to iron, blood and consecrated ground, Mackie is slowly dying in the human world. Mackie would give anything just to be normal, to live quietly amongst humans, practice his bass guitar and spend time with his crush, Tate.

But when Tate's baby sister goes missing, Mackie is drawn irrevocably back home to the fey underworld of Gentry, known as Mayhem, where he must face down the dark creatures, rescue the child, and find his rightful place - in our world, or theirs.