Captive Mate by Harper B. Cole

After Dr. Brand Delaney’s capture and rescue, the White Falls pack is desperate to know more about the secretive group Gecko Labs. But Gecko has beefed up security since their last break in, and getting in with brute force is impossible.
Eric Lundgren isn’t like most shifters, and definitely not like most alphas. He’s been content to pursue his interest in genetics, only returning to the pack once a month to satisfy his wolf’s need to associate with other shifters. But that is exactly what makes him the perfect wolf for the job. Alpha Alice Williams needs someone she can trust, who can apply to work at Gecko through the proper channels, and Eric is the only qualified candidate.
She convinces him to spy on Gecko, though he feels completely out of his depth, even more so when he finds his mate among the prisoners at the lab.
Omega Victor Cowen is often dubbed “the human calendar” by his cellmates. He spends his days in captivity counting seconds, minutes, and hours, trying to make sense of the passage of time when Gecko gives them no outside cues. The lights are on all the time; the meals come at irregular hours. The only way the prisoners have any clue what day it is is by Victor’s calculations and the arrival of new captives.
When Victor finds his mate, he feels beyond betrayed that the man is working with his captors. But Eric quickly finds a way to tell Victor he is there to help, and for the first time, Victor feels a sense of hope.
To earn the trust of Gecko Labs, Eric has to give them key information about the shifters, but doing so puts himself in more danger. Before Victor, spying on Gecko Labs was almost an academic challenge, but now his mission is all-too personal. The longer Eric stays, the harder it is to hide who he is and his connection to the captive omega, but he must, if he is to save him.