Okay, I came back to this and added a star to make 5 stars. Why? Because I'd read this book sometime ago, but can't get it out of my head, partly because it was so weird/unusual. So, I think it's worth 5 stars just for that reason.

A good story about the London Underground and some buskers who play music down there. One character is writing a history of the tube trains which is inserted throughout the book and was quite interesting. There is also bombings and young children riding on the outside roofs of the trains. This is a real page turner.