Frightmare

Fred Smith is spending the night in the office guarding a jewel for a rich client, and her only company is her latest date, a good-looking young man who happens to work for the client. It should be a dull shift. It isn't.

The jewel turns out to be a red herring, which is the episode being honest with you early. What matters is the night itself: the locked building, the man who is charming in slightly the wrong way, the sense that things are being moved around while Fred's back is turned. The office is the kind of setting that suits a thriller of nerves: phones that ring at the wrong time, a lift that arrives empty, a lock that clicks when it shouldn't. Before dawn she begins to doubt her own sanity, and the show does that slow unwinding well, mostly because it never tells you which fear is justified.

Don Houghton wrote it and James Hill directed. Leslie Ash's Fred carries almost the whole episode on her own, with Adam Bareham as Peter Standford, Patrick Newell as George Havant, Richard Austin as Mark and Rosemary Williams as the Doctor, while Jill Gascoine's Maggie, Rosalyn Landor's Pru and Don Warrington's Nigel drop in to keep the unit side alive. It went out in May 1985, midway through the first series. Patrick Newell, who plays the client George Havant, was Mother in The Avengers, so the episode borrows a face used to running the people around him.

It is a small, contained piece, and that is its strength. No car chases, no international gangs, just one woman in a building wondering if she can trust her own eyes. It is also a rare chance to see Fred work alone, without Maggie or Pru to bounce off, and Leslie Ash takes the opportunity. The title promises horror. And the real frightmare is closer to home: the slow realisation that the person you are alone with may be playing you.