Maybe Terrance Dicks was channelling his anger about the amount of rewriting the scripts needed, but this is surprisingly bloodthirsty stuff. Not only does the lovable old second Doctor rig up a solar ray gun to roast the Ice Warriors alive, but he condemns the Martian refugees to burn in the Sun’s orbit before calmly revealing to Slaar the extent of his genocide, and tops it all by killing off the last survivors. Priti Patel would be impressed. But then, the Ice Warriors were evil men.

On the one hand, the episode satisfactorily ties up all the plot elements: the seeds of death are washed away; the Martians are incinerated; T-Mat will be repaired and reprogrammed to safeguard it from future hacks, and Eldred will campaign for a common-sense rocket programme. On the other, the Ice Warriors are almost entirely passive in the final episode, largely awaiting their fates, as everything set up in the previous episode falls neatly into place here. The lack of eleventh hour complications, and the fact that the Martians spend the episode waiting around – just as they did in The Ice Warriors – tends to make the Doctor’s massacre seem more brutal than similar treatment of the Cybermen, the Daleks and the Krotons in more desperate circumstances. Plus, like The Invasion, the reliance on dots on a monitor to represent the fate of the Ice Warrior fleet looks cheap rather than ingenious.

Still, there are some great lines (Miss Kelly’s response to the questions ‘What kind of car?’ pretty much sums up my own attitude: ‘I’ve no idea but it’s got four wheels and it goes’), Troughton is on top form, sitting down at the T-Mat control bank like a concert pianist ready to play, and Alan Bennion gets his best moments as Slaar, practically rolling his eyes as the Grand Marshal chastises him for killing Fewsham; panicking as the fleet veers off course, and physically reeling as the Doctor lays out the terrible depth of his failure.

As a whole, the serial is hugely under-rated, suffering, like the rest of Season Six, because it survived to be watched and dismissed in favour of the safely “lost” classics. Actually, it’s definitely better than the Season Five six-parters, barring The Web of Fear and perhaps The Abominable Snowmen, and much more consistently entertaining than The Dominators or The Invasion. With the end in sight, Troughton seems to be enjoying himself pushing the limits of both the comic and ruthless aspects of the Doctor; Hines and Padbury continue to be a winning team, and Michael Ferguson directs this even more effectively and inventively than Camfield did The Invasion. Even if it’s not once of the iconic Troughton stories, it still deserves more love than it tends to get.

Next episode: “The Space Pirates”