The breath of demons - Stephanie Baudet

This is one volume in the Moonstones series of stories for 8 to 12 year olds. Each story has an element of mystery or adventure, with a strong storyline, and is suitable for the multi-cultural classroom.
When Mike defies his father and takes part in the charity walk to London, he finds himself retracing the route of a 17th century post boy. Flitting without warning between past and present, he realises that the dangers facing Will have their 20th century equivalents and, as they near their destination, Mike has to come to terms with both Will's fate and his own future.