Safe At Last by Megs Pritchard

Escaping the lab that had held him captive, Holden had no idea what lay ahead. Freedom had been his sole focus. Once he reached Morefield Village, he would have the time and space he needed to figure it out. What he hadn’t considered was meeting his mate.
When Rand helped the shifters who’d escaped the lab, the sweet scent of his mate startled him. Too old and scarred to have a mate, finding one had been the last thing on his mind, but he wasn’t stupid either. You only had one mate and he wasn’t going to let his slip through his fingers.
As their relationship progressed, both Rand and Holden learned to trust the other. Then Holden collapsed.

Could Ran figure out what had happened and save his mate, or would he be helpless and watch him slip away?