It is the locale that makes the atmosphere of this book so successful. The story is set on a R.A.F. airfield on the marshes near the North Lincolnshire coast. It was used as a Coastal Command base during the Second World War. Two boys are at the centre of the experience and a series character nicknamed 'The Blue Falcon' is the nominal hero.
Mists sweep in from the sea and, for a while, make it plausible that unknown airmen are able to come and go within the perimeter of the secure base without being apprehended. The series of events that set everybody's nerves on edge are so violent and unexpected that it is hard to make any sense of what is being attempted by the people behind the 'so-called' haunting. A small dog is killed and mutilated without any logical explanation. A man in R.A.F. uniform in the mess responds to a challenge by lashing out and escaping into the rapidly approaching mist.
Most of the action takes place at night and the personnel on the base are in the grip of rumours and gossip about how old burial mounds have been responsible for the outbreak of sudden and violent activity. The tension is screwed up a few more rachets to breaking point when the vicar's daughter disappears into the mist and then the Blue Falcon himself is reduced to a helpless victim by a ninety-nine percent effective attempt at strangulation.
No sooner does the legitimate clandestine activity of the secret base become clear to the reader than the sudden and devastating attack is launched. Only the quick-thinking of the young hero leads to the apprehension of the malefactors and an explanation of their subterfuge.