Colonel White's curiosity is piqued by a UFO report from the Scottish Highlands where an elderly lady, Mrs Mackenzie, claims to have seen green lights hovering over the Grampian Nuclear Power Station. Scarlet is dispatched in an Albatross to investigate the plant while Harmony takes a break from the nearby Spectrum Flight Training School to visit Mrs Mackenzie, accompanied by Spectrum Cadet Johnson. Arriving at the power station, Scarlet is assured by the Head of Security that not one of the plant's 400 personnel has seen anything unusual, but at Mrs Mackenzie's cottage, Harmony discovers that neither of her companions are what they appear to be...