Thriller!

Supernatural horror story from the classic early Seventies series created by Brian (He Also Did The Avengers) Clemens. Among the star-studded cast we find Patrick Troughton, who starred in Doctor Who (1966-9) and later played Father Brennan in The Omen. Then there's Ed Bishop, with his natural hair, who was famously fair-headed as Ed Straker in UFO. Cec Linder, a Canadian playing the US diplomat here, whose first big UK role was as the heroic Dr Roney in the classic TV serial Quatermass and the Pit (1960). Last but not least, the evil nursey is played by Diana Dors, famous as a blonde bombshell in her youth but here showing real talent for insidious menace. Oo-er. Merry Christmas, one and all.

And, if you were wondering why so many American characters feature in this vert British show, it was simply because it was always intended for the US network market.