Alex Walton 
The Non Talking Boy 3 

This book is about a boy named James who goes on an adventure around London but as he’s walking around London he comes across this mysterious creature in a cave, and the cave is in Oxford Circus.

and nobody knew how the cave got there because there’s no other caves in London and that cave is from 1788 and was built in London to keep out the Rats from entering and destroying the city.