Krissie and Sarah have been best friends since they were children. But when Krissie accidentally becomes pregnant following a drug-fuelled dalliance in a Tenerife toilet cubicle, after Sarah and her husband Kyle have been trying unsuccessfully for years to have a baby, cracks start to appear. A walking holiday around Loch Lomond is make or break for their friendship - and then one night friendship turns to betrayal, and betrayal turns to murder...