For the people who live on the banks of the Thames, the river is a living, breathing thing. It can take your treasures. It can hide your treasures. And, sometimes, it can give them back.

Bo and Billy are two children who have never met. Billy is an orphan. Bo's dad died when she was small and now her brother is off to war. Both children are poor, but they have each found half of a priceless treasure, given up by the river. A treasure which - when the pieces are reunited - holds the power to give back to one of them the most precious thing they have ever lost.

But should the treasure be put back together again? And why has the river given it up now?