From the back of the book Flashing lights are seen from a distant tower, and Philip, Lucy-Ann, Dinah and Jack are quick to investigate. Son they discover a sinister plot concealed within its hidden rooms and gloomy underground passages. What is the secret of the old castle on the hill, and why are the locals so afraid of it? Do you dare help the Adventure Squad investigate the lonely castle? With your help some sinister secrets could be unveiled. But tread carefully. If you make the wrong choices, the intrepid adventurers could be in deadly peril...