In late December of 1980, the Royal Air Force bases of Bentwaters and Woodbridge were temporarily plagued by a series of mysterious UFO sightings occurring in the old Rendlesham Forest surrounding the bases — sightings which included visual observations by military officers; sightings which were never solved. Now, not only have those sightings resumed, but residents of the Rendlesham Forest area in Suffolk are up in arms: one of their neighbors, one John McFarlane, has died, apparently frightened to death by a close UFO encounter. The problem is that RAF Bentwaters and Woodbridge are not abandoned as the residents believe, but are now high-tech research facilities, literally underground. The British government fears that someone may be onto this fact and out to expose or infiltrate the bases.

Meanwhile, Mr. Sherlock Holmes and Dr. Skye Chadwick have formalized their personal relationship and left snowy Colorado to come to London on a vacation. A vacation — or, in Holmes’ terms, a holiday — which was a special Christmas present from Skye, so that Holmes might not only introduce his companion to the city he once called home, but that he could also see how that metropolis has changed since his time. But their holiday is rudely interrupted when Her Majesty’s Secret Service calls upon them to act as special independent investigators in the UFO death.

What is the UFO? Why does Skye find it familiar? Who — or what — killed McFarlane? And how can the pair do what even Her Majesty’s Secret Service could not?