Bo and Billy have both discovered treasure on the shore of the river. 

The silver, bejewelled disc would buy all sorts of comfort and security for her family should Bo Delafort decide to sell it. It's the middle of World War II and her brother Harry is away fighting. 

Bo meets Billy, though, and for him the treasure means much more. He is an orphan and his mother lived hundreds of years earlier. The disc would reunite mother and son.

If their two pieces of a single coin at placed together, they will have the power to retrieve the most precious thing they've ever lost. But should they do it? What might be the consequences? Why has the river yielded up this treasure now? Should they consider the greater good rather than their own desire for hope and healing? Who is most deserving of their desire? And how do they protect the treasure from the machinations of Lord Muncaster and Avery, both of whom also want the magical power.

It's a beautiful book full of jeopardy and mystery. The characters are great and the atmosphere of wartime London is vivid and powerful. 

This is the first children's story from the author of 'The Miniaturist'.