‘Wullie, can you no send over a few haggis?’ D’ye ken if we’re in Scotland? I love how Robert Banks Stewart, a Scottish writer, embraces the cliches, reminding everybody that his namesake Brigadier Lethbridge-Stewart is of Scottish heritage. Also, how token Sassenach Sarah, who initially treats this all as a bit of colourful regional fluff, is constantly shown up for being so patronising, culminating in a lovely moment when she puts on a Scotch accent to answer the phone and has the smile wiped off her face when she learns Harry has been shot.

This is the most atmospheric story in years – certainly since The Dæmons. It opens with a night-time attack by something vast and terrifying that wrecks an oil rig, full moon in the sky over the dark and lonely water before flipping to the Doctor, Harry and Sarah striding across the convincingly empty vista of Tullock Moor. Later, there’s a wonderful sequence of Angus MacRanald telling Sarah eerie stories of the moor while they’re watched by something orange and alien in a moistly organic control room, all punctuated by the mournful wailing of bagpipes.

There are some similarities to Robot – the Doctor’s discovery of a giant tooth mark feels like a replay of his discovery of a squashed dandelion – but this is very much more chilly, not least because Tom Baker plays the Doctor as being genuinely peeved at being summoned back to Earth, chafing to be free of his tedious responsibilities to UNIT, not even glancing at his old friend Benton as he issues instructions. The scene where Caber shoots Harry and Munro on the dunes is beautifully done – Munro, staggering from the sea, framed against the sun; Caber carefully targeting him. The Zygon attack on Sarah is a genuine jump scare, a sudden reveal of the blobby alien, just enough to give an impression before the credits kick in is one of the best horror cliffhangers in ages.

Next episode: Terror of the Zygons – Part Two