This is a really disappointing end. A lot of the elements should work – the Doctor joining forces with Vaughn to defeat the remaining Cybermen; the UNIT attack on the Cybermen’s last outpost, and the destruction of the Cyberman fleet. But in the end, there are just too many disparate elements (and Sherwin keeps throwing in more) that means even Camfield’s attempts to make it all dynamic can’t hide the fact that this is overly busy.

There are some nice moments. Vaughn finally declaring his interest – the world has too many conflicting ideologies and would benefit from strong, central leadership (his, naturally), is positioned against UNIT’s ability to unite Eastern and Western Blocs for the sake of humanity. And the idea of the Doctor convincing the villain to help defeat the monsters feels like one that will be revisited to even greater effect when the Master arrives.

But Vaughn’s death – shot and left dangling on a railing in the background – is offhand for such a vivid character. Packer gets a better exit, which is pretty unforgivable. He doesn’t even seem to die for anything – it’s UNIT that deactivate the signal to the Cyberman fleet. The big battle scene at the IE factory feels like The Web of Fear‘s Covent Garden sequence done bigger, and prefigures all those big Season Seven and Eight “Action by HAVOC” climaxes, with the wonderful addition of Troughton leaping about like Buster Keaton. But sadly, The Invasion‘s actual climax is a couple of dozen soldiers waiting anxiously to see whether some dots on a screen disappear or not. Camfield again tries his best, but it’s beyond anyone to make some men shouting ‘We’ve done it!’ stand in for an actual showdown. Bafflingly, the Doctor doesn’t even get a goodbye scene with the Brigadier.

As a whole, the serial has loads of good elements, taking the best bits of The Web of Fear, adding in a more interesting villain and UNIT. While all of them will be done better in the coming years, this is definitely a seminal Doctor Who story. It’s also hugely frustrating that it takes four episodes to properly get going, and then drops the ball at the last moment. Still, Episodes Five and Six are great and Episode Seven is a masterpiece; Tobias Vaughn remains one of the show’s most effective villains; the Cybermen have rarely looked better; Wendy Padbury gets her best material yet; Nicholas Courtney nails the Brigadier so well that he’s become a more enduring character than several of the Doctors. If the whole is more than the sum of its parts, it’s still worth appreciating just how enduringly fantastic some of those parts are.

Next episode: The Krotons