Celia Rees - City Of Shadows

Synopsis: 
It's the summer of his twelfth birthday, and Davey, his sister 
Kate, and his twin cousins Tom and Elinor join the 
hoards of tourists eager to catch a glimpse of the 
legendary underground city in Davey's hometown. A 
harmless trip. Just a bit of fun. But for Davey, it's 
the start of a nightmare--and a long, terrifying battle 
with the dead...