Zom-B Underground by Darren Shan is the second book in the Zom-B series and the sequel to the titular book, Zom-B (http://www.bubblews.com/news/9298652 ).

Zom-B finished with a couple of surprises. The first was that B's real name was Becky, and that the shaven headed thug was a teenage girl. The second was that, after finally defying her father and rejecting his racism - after getting another kid killed at his request - B herself also died, at the hands of that same kid.

B is now a zombie. Several months after the attacks in London, though, she regains consciousness - although she's still dead. It seems that some zombies regain their intellect and she, and some others who have, are being experimented on in a, presumably underground, facility.

B has to try and work out what is happening. Which isn't easy, as her captors regard her as a monster, albeit an intelligent one, and are deliberately withholding information.