When Jack sees mysterious lights glimmering at midnight on the moors above Castle Key, the friends know there's a new mystery to solve in this 14th adventure of the series.

Something strange is afoot on the moors above Castle Key - sinister noises, lights in the sky and mysterious figures moving in the dark. Are aliens invading, as Jack suspects? Could it be smugglers, as Emily thinks? Or is there another explanation? Scott, Jack, Emily and Drift the dog are on the case!