Unleashed By the Guardian by Kathy Lyons

He lost himself to the wild. She’ll drag him back to save her brother.

Simon Gold spent ten months as a grizzly, forgetting what it means to be human. When Alyssa Ursun tracks him down and puts five bullets in his chest, the forced shift back nearly kills him—and wakes something darker than the bear.
Alyssa doesn’t care that Simon can barely speak. The Detroit Flu is turning her brother into a monster, and Simon’s the only shifter who might understand why. Getting him to Detroit means teaching him to be human again—one dangerous mile at a time.
But the virus isn’t natural. Failed shifters are dying, and when Simon’s forced into a brutal challenge for alpha, defeating his enemy unleashes the feral dominance he’s been fighting. Only Alyssa can pull him back from the darkness.

She refuses to submit to a beast. He needs her strength to stay human.
Together they’ll uncover the truth—if Simon doesn’t lose himself forever.

Originally published as Alpha Unleashed