Face at the Window by Julie Ireland

There's not a lot available about author, Julie Ireland, on the internet, but she has written a few books for children. This novel is full of suspense and if you like mysteries, you will most likely enjoy this one. The decaying old mansion, Wundilla, had always been given a wide berth, especially after the owner, Miss McKenzie’s week-old corpse had been discovered, full of maggots. It was supposed to be empty but Toby found it wasn't. Whilst trying to escape some local bullies, a strange girl called Leanda comes to his rescue. She has been using the old barn as her private sanctuary, and inside the house itself Toby discovered a boy and his mother, both ill and both on the run.