The Siege (Arisen #13)

THE BATTLE FOR THE GAP 
In the north, the collapsed section of the Wall is defended only by the decimated remains of 2 PARA. Even reinforced by Jameson and the exhausted Royal Marines of One Troop, it's a doomed delaying action at best - and the last choke point in the entire ZA faces an incoming tide of dead stretching to the ends of the Earth... 

THE RACE FOR THE CURE 
Finally united, Dr. Park and Aliyev the Kazakh, supported by Pred and Juice on a mission out into a London falling into chaos, struggle to perfect the vaccine that will preserve the dwindling flame of humanity - and to weaponize the designer pathogen that might just destroy the rampaging armies of the dead... 

THE DEFENSE OF THE ALAMO 
Hunkered down at CentCom, the unified ranks of our heroes, led by Ali and Fick, work furiously to fortify and reinforce what will be humanity's final fallback position - forever. But it may be over before it begins, as a runner invasion from the south hits even before the great wave of death coming in from the north... 

Brotherhood. Duty. Desolation.