Threadborn. The Threadborn Trilogy, #1

The dead man in his blood has been waiting fifteen years to wake up. Soren Voss has spent his whole life hiding his left hand - the one with dark veins that pulse like something alive beneath his skin. In Millhaven, Ohio, he's the quiet kid with the bad hand. Nobody knows what lives inside him. Not even Soren. Then a stranger arrives and pulls Soren into the Loom - a hidden school of threading, where practitioners manipulate invisible forces that bind the world together.
For the first time, Soren has a name for what he is. For the first time, he belongs somewhere. But the Loom has secrets. The dark veins aren't a gift - they're a seed. Inside Soren's blood lives a fragment of Erasmus Thane, the most dangerous threader who ever lived, a man who died fifteen years ago and has been rebuilding himself inside a boy's body ever since. Now the fragment is waking. And Soren must decide what he's willing to destroy to survive - including himself.
Threadborn is the first book in The Threadborn Trilogy - a dark fantasy series about power, identity, and the monster that loves you most. For readers of Leigh Bardugo, Holly Black, and V. E. Schwab.