Silver Stranger by Iona Strom

Alyssa
I should have been worried about not flubbing up my first day as an intern in NASA’s undergraduate program for planetary research. Instead, I was terrified of which alien prisoner I was bought to pleasure first. Anyone but the silver male they called the Berserker. He terrified me the most.

Drekkor
Stolen from the Trisess Forest on my home world by little gray freaks, I was sold, then forced to fight in an arena for the pleasure of others. Losing was a death sentence. As a seasoned warrior of Valose, I had the fighting skills to keep myself alive no matter what monster they pitted against me. To the chagrin of my jailers, none stood a chance.
Then she was tossed into my cage, a curvy distraction they thought would soften me. Instead, she triggered a biological response that should not be possible. That a female of another species could breathe life into my ancillary heart seemed impossible, but the adrenalyne that pumped through my veins might be the fuel I needed to rescue us both.