The Devil's Fortress - Dale Brown

After saving the US from a Russian nuclear attack in the bestselling Weapons of Opportunity, Nick Flynn returns in what could be his most dangerous mission yet. Former US Air Force officer Nick Flynn joined the clandestine Quartet Directorate to continue its long-standing mission: to act decisively against serious threats to the free world. And with the backing of Russia's authoritarian president, no threat is more deadly than that of Pavel Voronin and his mercenary Raven Syndicate. Twice they have almost succeeded in bringing the United States to its knees, only to be stopped at the last moment by Flynn and his team of highly trained operatives.
But Flynn knows it's only a matter of time before one of Voronin's plans to cripple the US bears lethal fruit. And so, taking the Russian oligarch permanently off the board is now his number one priority. Operating undetected deep in hostile territory and fighting their way through Voronin's extraordinarily tough defenses will require every ounce of skill, dedication, and daring that Flynn and his small force can muster. The slightest error could be fatal for all of them—and, ultimately, for millions of Americans.
With the clock ticking, and dangers mounting on all sides, it's up to Flynn and the others to finish Voronin before it's too late. In this all-or-nothing battle, victory is the only acceptable outcome—no matter how high the cost!