Resonance surge / Nalini Singh.

Pavel and Yakov Stepyrev have been a unit since their birth, but now Pavel's life is veering in a new direction, his heart held in the hands of Arwen Mercant, a Psy empath - and the only man who has ever brought Pavel to his knees. This is it. A point of irrevocable change. For Pavel, for Arwen, for Yakov - and for another pair of twins whose bond has a far darker history. A low-gradient Psy, Theodora Marshall is considered worthless by everyone but her violently powerful twin, Pax. She is the sole person he trusts in their venomous family to investigate a hidden and terrible part of their family history - an unregistered rehabilitation center established by their grandfather.