Tunnels, by Roderick Gordon and Brian Williams

Started listening to the recording of this in November and ended up checking the book out to finish it this week.

Fun book. Will and his father spend their time together excavating London, making discoveries about the city's past. Then his father disappears after some mysterious tunnels are found, and Will follows him into an underground city built several hundred years ago.

Quite creepy in parts, and the first of a series, so I will have to go find the second book now.