This is the first Doctor Who script by Don Houghton, who also wrote Hammer Horror movies (including the excellent Satanic Rites of Dracula), Sapphire and Steel and Ace of Wands. After 14 weeks largely written by Malcolm Hulke, this has quite a different tone, even if the setting – a scientific facility beset by unexplained issues – is the same. Professor Stahlman is very much in the vein of Dr Lawrence – a choleric and overbearing director, with no time for the civil servants or “experts” that continually seek to interfere with his work. But whereas Doctor Who and the Silurians and The Ambassadors of Death kept its monsters mysterious, this episode pretty much tells us everything we need to know up front: Stahlman is drilling into the Earth’s crust; the drilling is releasing a weird green ooze; the green ooze turns anyone it touches into a green werewolf.

With the threat fairly plainly sketched, Houghton spends more time introducing his cast of fairly vivid characters. Aside from Stahlman there’s the fussy Sir Keith Gold, a much more cautious and clubbable man than the director. There’s Petra Williams, Stahlman’s icy P.A., and there’s Greg Sutton, a bluff drilling expert flown in from Kuwait to advise on the project. All are clearly and concisely presented, as if this were the pilot for a series set in the high-powered world of business, and the tensions between them – Greg fancies Petra, but is a bit of rough; Petra probably fancies Greg but idolises Stahlman; Stahlman hates everyone – are all entertaining enough, and quite soapy, which is maybe fitting given Houghton’s background writing for the medical soap Emergency – Ward 10.

On top of this, the Brigadier and the Doctor get some amusing banter about the Brigadier’s old regimental photo, and the Doctor exchanges pleasantries with a UNIT solder, gossips to Liz about the politics of the facility and opens up about how he feels being confined to Earth without his TARDIS: like a ‘shipwrecked mariner’. This is all hugely entertaining, and like nothing we’ve seen for years – you’d have to go back to the highly serialised early Hartnell episodes to get anything like this level of everyday interplay between the characters.

Luckily, it’s not just soapy chat though. There’s a killer on the loose in the facility. Douglas Camfield pays a familiar trick of cutting from a raised spanner swooping down towards a scientist’s head to Benton’s hammer bashing in a nail to imply more violence than we see. And the idea of a human being being physically changed into an alien organism is both straight out of The Quatermass Experiment, and a precursor to quite a lot of Doctor Who serials from now on. This is a very entertaining introduction to the new serial.

Next episode: Inferno – Episode 2