Showing Caressed by Ice by Nalini Singh

As an Arrow, an elite soldier in the Psy Council ranks, Judd Lauren was forced to do terrible things in the name of his people. Now a defector, his dark abilities have made him the most deadly of assassins - cold, pitiless, unfeeling. Until he meets Brenna . . .

Brenna Shane Kincaid was an innocent before she was abducted - and had her mind violated - by a serial killer. Her sense of evil runs so deep, she fears she could become a killer herself. Then the first dead body is found, victim of a familiar madness. Judd is her only hope, yet her sensual changeling side rebels against the inhuman chill of his personality, even as desire explodes between them. Shocking and raw, their passion is a danger that threatens not only their hearts, but their very lives . . .