Darren Shan 
Zom-B: Volume 3 City [EPUB ebook] 
ZOM-B Series, Book Three

Exhausted from the terrible conflicts and carnage of Book Two, B staggers out of the darkness of the underground complex and into a city overrun by zombies. But the battle is far from over, as the living, dead and an army of mutants continue their fight in the streets of a transformed London, and B battles moral dilemmas and a growing sense of hopelessness at every turn.