In the Nick of Time

YA. Charlie is out in the woods on her own one day when something mysterious happens - she walks along a row of stones on the forest floor ... and finds herself in another age. She has somehow slipped back to 1955, and is now, in the same woods, on the site of an open-air school for sick city children. No one believes her tales of the world she's come from, and her mobile doesn't work. A friendship with another pupil provides the key - is Jack more than he seems.