A nice middle grade novel but the ending was just too unbelievable for me. I would have been OK with the first element (that the key he found in England originally came from Sweden and he has happened to find a curator who believes him etc) but not that they then find the lock into which it fits....
But really the "find" plot isn't the main element of the story. The book is really about friendship and refugees and caring for other people in their moments of need.

The characters were mainly convincing, especially Judy and William. William has special educational needs (exact diagnosis isn't given but probably somewhere on the autistic spectrum from his description) and Judy lives alone with her father on a canal boat. She is half Iranian and a mathematical whizz. I found Stefan and his Formor less convincing; they are just too kind to complete strangers! Perhaps that's just the cynic in me... ( )