When curious blue rays light up the sky over Cockermouth in a mysterious pattern, young sisters Mae and Isla Donaldson face shape-shifting adversaries. With the help of their irascible Granddad, the girls discover how to break a secret code and unlock the truth about a group of special agents who disappeared from a Lake District beauty spot while investigating UFOs. The girls must prove their suspicions about the glamorous new people in town before it's too late.