Boisterous Uncle Bill comes to town, bringing trouble with him in the form of a brutal mercenary tracking a diamond smuggler. With their ESP and deduction skills, Mae and Isla find themselves caught up in an international terrorist plot involving their parents' workplace, risking a nuclear catastrophe that could destroy them all. Can they work out the purpose of a peculiar device they found before it's too late? Meet the Donaldson girls - primary schoolers and detectives. Mae, clever and very, very proper. Isla, a wild, artistic soul most at home wandering the fells of England's beautiful Lake District. They are united by an uncanny ability to share their thoughts.