And I Darken by Kiersten White

'Lada has a sense for power -

A princess unlike any you've known before; ruthlessness is the key to her survival.

the fine threads that connected everyone around her,

Her brother Radu is everything she is not: beautiful, introspective and delicate.

the way those threads could be pulled, tightened,

At first, Lada takes Mehmed for an enemy. He is, after all, son of the sultan holding her captive.

wrapped around someone until they cut off the blood supply.

Their three lives balance on a knife edge, and the ties that bind them together will be stretched to breaking point.

Or snapped entirely.'