Gran and the Tied Man

What or who is the figure in the graveyard? John, Robbie, Alex and Paul find they need Gran's help again. Hiding facts from parents and nosy neighbours makes life difficult. The transporter may be needed again and no one knows where they might end up. Are they brave enough to face enemies with weapons? Does the ruined fortess hold a key to the mystery? Weird! Scary! Luckily, Grandpa has been married to Gran for a long time and should be prepared for anything.