The Replacement

In Brenna Yovanoff's The Replacement, Mackie Doyle has spent sixteen years hiding what he is: a changeling swapped for a human baby by the Gentry, tunnel-dwelling creatures ruled by a tattooed queen, and fatally allergic to iron, blood and consecrated ground. He wants nothing more than an ordinary life and a chance with his crush, Tate — but when Tate's baby sister is taken by the same forces that once took him, Mackie is drawn back into the underworld he was raised to escape.