Evernight

Holly Evernight belongs to a very special family of inventors. They have nobly served the Society for the Suppression of Supernaturals for generations. And Holly may have the most special creative powers of them all. But her skills are about to be tested as she tries to save the life of a half-man-half-machine whose clockwork heart is ticking down to the bitter end... William Thorne was a rebel, a hired assassin for the SOS's greatest rival, before he was taken, tortured and transformed.
Now his mind and soul battle with his body as he becomes less and less human. But the true fight for his humanity will be waged within his heart.