Alamo: The Retreat, Book 4 (Unabridged‪)‬

During the long retreat out of Philadelphia, First Battalion arrives at High Point Special Facility, the Alamo of the US government. Lt. Colonel Lee secures the fort built around the facility but learns of an outbreak in the underground bunker, where the US government is hiding. The president has been infected. 

While thousands of laughing infected lay siege to the facility, Sergeant Muldoon, Corporal Rawlings, and a platoon of lightfighters go deep into the bowels of the earth on a deadly mission: terminate the president of the United States.

The president is waiting.