The Peacekeepers. The Citadel. Book 6.
In the Guadalupe Mountains of Texas, the peacekeepers discover the base for Phoenix Rising, a secret government project that planned to utilize the work of the development team who’d designed the Peacekeeper. Inside that citadel, they discovered an aircraft unlike any other they had ever seen. Calling on all of their resources, the peacekeepers race to prevent a nuclear strike on American soil.