The Melody and the Master by Sarah M. Cradit

Her song is death. His offer is life.

Disappear into this twisty tale of a ruthless heir and the sheltered, gifted orphan he chooses as both his wife and his greatest weapon against a growing list of enemies.
Siofra has lived her entire life in isolation, terrified of her unrestrained dark magic. Then the unthinkable happens, and she and her brother are imprisoned for murder.
Before the law can deliver their punishment, the siblings are rescued by a mysterious benefactor, whisked away to a glamorous manor in the far north, where everyone treats them like a prince and princess.
Shadowfen Hall, and the surrounding forest, keeps a wall between Desemir and his rivals. His lack of heir leaves him vulnerable, but to marry within his peerage would ignite the very coup he needs to avoid.
Siofra and Desemir’s needs conveniently intersect. She needs protection for herself and her brother. He needs a wife and children to secure his legacy.
If it all seems too good to be true, it is.
Because everyone knows darkness can only be soothed, not contained.