P.R.O.B.E.: Ghosts of Winterborne
Roots: The X-Files and Satanic ritual films. Again. Purcell quotes T. E. Burroughs.
Goofs: Why does Liz have a seizure when Andrew/Greatorix stabs his victim? [She's presumably somehow psychically linked to them due to the events of The Devil of Winterborne, but it's poorly explained].
Dialogue Disasters: Greatorix goes all "Thou dost well to fear me, woman" at the end.
Continuity: Christian's body has recently been discovered by the motorway, months after the events of The Devil of Winterborne. Greatorix's Grimoire was sold to a private collector after Purcell's trial; it contains the knowledge required by Greatorix to resurrect him. The book is made of Greatorix's own skin, and is in effect his own body; he needs to recombine with it in order to be resurrected. His ghost (in the shape of Christian) is haunting, possessing and controlling Andrew in order to achieve this end. He apparently has a limited time left in which to complete the ceremony [possibly as a result of his host's death]. Greatorix eventually manages to possess Purcell via the grimoire; he dies for good when Liz burns the book, as does Purcell.
At the start of the story, Liz has just been investigating a poltergeist, which turned out to be a policeman's joke. She visits her father's grave, close to Winterborne (The Devil of Winterborne).
Links: The Devil of Winterborne
Location: Winterborne School and surrounding area, Surrey; Whitehall, London; [c1996 and several months after The Devil of Winterborne].
The Bottom Line: More overtly occultist than The Devil of Winterborne, the final PROBE story ties up various loose ends and makes for a fairly satisfying (if rather short) conclusion.