Wolfsbane by Ronie Kendig
From Goodreads.com:
Former Green Beret Captain Canyon Metcalfe is unnerved when Nightshade is sent to a South American jungle that holds an eerie similarity to a dark tragedy from his past. Addicted to painkillers, Canyon struggles to hide his secret. Escorting Danielle Roark, a demolitions expert who knows the location of a secret nuclear weapons silo, proves treacherous when they’re ambushed and captured. Rescued, Canyon is furious to discover Dani was left behind, intentionally—because she’d unearthed blame that lies at the feet of many on the Hill, including her own father. Armed with truth, they must fight their way back to the States and freedom.
