Feehan, Christine. Leopard people series.

"Gorya Amurov might be known as his family's peacekeeper, but the leopard inside him wants nothing more than to claw to the surface and unleash hell. A harsh life has shaped him into a vicious fighter with a calm exterior, but Gorya knows it's only a matter of time until he loses all control...Maya Averina has spent years hunting the criminals who destroyed her life...She keeps to herself, stays under the radar...But with her body burning up...an ambush takes her by surprise. Now she's trapped, an unmated female shifter about to be sold off to the highest bidder. Maya is ready to fight her way out--until the most dangerous, powerful man she's ever encountered arrives to set her free"--