Marked

When Lex is taken from her teammates, she expects to be eliminated or harvested for Project Enhanced. Instead, Lt. Col. Jasper Caswell, leader of the black ops group pursuing them, has marked her as his mate. It's a fate worse than death, and she is desperate to escape. The mysterious and handsome Aidan, who works in support services, seems like her best chance of doing so. With his help, she discovers what the group really wants from the shifters who have eluded them. She thinks she has also found her mate, but Caswell is determined to claim her. To have any kind of future together, they'll have to find a way out of the secret base-and counter the mating bite on her neck that allows Caswell to track her…
"Marked" picks up just shortly after events in "Relentless," and it's highly recommended you read that before reading this book. I attempted to make this book function as a standalone, but reading all parts in order will enhance your reading enjoyment.