The Secret in the Farmhouse +Audio

Four friends - Alex, Dan, Matt and Hannah - are spending a week in the country on a school trip. In an old, empty farmhouse, they discover hidden boxes full of stolen things. They tell the police what they've found, but someone makes sure the police don't believe them. What has happened to the boxes? Who is keeping the secret in the farmhouse? When the four friends try to come up with some answers, they find themselves up against a group of dangerous criminals.