City of Halves by Lucy Inglis (author)

London. Girls are disappearing.
They’ve all got one thing in
common; they just don’t know it
yet .
Sixteen-year-old Lily was meant
to be next, but she’s saved by a
stranger: a half-human boy with
gold-flecked eyes. Regan is from
an unseen world hidden within our
own, where legendary creatures
hide in plain sight. But now both
worlds are under threat, and Lily
and Regan must race to find the
girls, and save their divided city.