The Poison Sky is the fifth episode of the fourth series of Doctor Who and the second half of the Sontaran two-parter. ATMOS gas is choking the Earth, UNIT’s counter-attack struggles, Donna ends up stranded on the Sontaran ship, and the Doctor builds a device to burn the poison out of the sky.
The piece covers the everyday-apocalypse imagery, UNIT’s bad day, Donna being tested, and the surprising ending for teenage genius Luke Rattigan. It lands on a competent but conventional hour with a better heart than its plot, and gives the episode 3/5.
The second half of a two-parter has one job: pay off the mess the first half made. The Sontaran Stratagem left us with four hundred million cars pumping poison into the sky, an old man sealed in a gassing car in his own driveway, and a fleet of very short soldiers in orbit having the time of their lives. “The Poison Sky” does that competently rather than brilliantly. It’s the most conventional hour of the season so far, all corridors and countdowns and soldiers shouting into radios, but it gives Donna a properly hard night, it finds an unexpectedly moving ending for its most irritating character, and it lets the Doctor be quietly, seriously angry about something worth being angry about.
Axes and Atmospheres
We left Wilf choking in a locked car, and the resolution is perfect: Sylvia Noble puts an axe through the windscreen. It’s a brilliant little beat, the mother who has spent two episodes being witheringly unimpressed by everything turning out to be the one who runs at a problem with a hatchet. The Nobles continue to be the best supporting family the show has had since the Tylers, and I’d happily watch a whole spin-off of Sylvia just being appalled at things.
The scale of the threat is well handled. This isn’t an invasion fleet in the sky, it’s every car on Earth belching poison at once, cities vanishing under yellow fog, hospitals filling up. The Sontarans aren’t conquering the planet in the usual sense, they’re converting it, turning the atmosphere into feed for growing clones, because a war with the Rutans needs bodies and Earth is a conveniently placed nursery. Humanity isn’t even the enemy. It’s just in the way of the breeding programme, which is a properly dismissive kind of villainy.
The imagery earns it too. There’s a genuinely unsettling stretch where the streets simply empty, abandoned traffic sitting in the road, yellow fog rolling between semi-detached houses, an entire country told to stay indoors. It’s a very British sort of apocalypse, all civil-defence broadcasts and people taping up their window frames, and it’s considerably more effective than the space battle that follows it. The show has always been good at catastrophe in suburban terms and this is a strong example, and I’ll take it over a fleet of spaceships any day of the week.
UNIT’s Bad Day
The military response is the most interesting failure in the episode. The Doctor warns UNIT off engaging the Sontarans and, being soldiers, they engage the Sontarans, and it goes about as well as he said. Even the launch of a nuclear missile gets stopped, with Martha’s clone helping the Sontarans from inside UNIT, which is when he works out what they’re really protecting. Colonel Mace’s counter-move is bringing in the Valiant, the huge flying carrier the Master used in The Sound of Drums, and it’s a nice piece of continuity. The sight of that thing rising through the fog to open fire is the best image in the episode.
The Doctor’s relationship with all this stays prickly, which I appreciated. He works alongside them, he uses what they can do, and he never once pretends to like it. The argument the two-parter started about whether his contempt for soldiers is entirely fair doesn’t get settled here either, and the show is right not to force it. After the cold fury of Planet of the Ood it’s interesting to watch him angry in a different way, this time at people who ought to know better and are doing it anyway.
Martha, meanwhile, spends most of the hour in a tank. The Doctor finds the real one inside a Sontaran cloning device and wakes her up, which kills the clone, and it’s a strange little scene watching Martha and her own duplicate. The clone thread doesn’t amount to a lot in the end, but it gives Freema Agyeman something to play besides explaining the plot.
Staal deserves a mention because he’s the reason the Sontarans still work as villains at all. Christopher Ryan plays him as a man who genuinely believes every word of the warrior creed and finds the Doctor faintly pitiful, and the scenes where the two of them trade insults across the ship are the sharpest dialogue in the hour. But the second half does ask them to spend a lot of time barking orders and being shot at, and that’s where the menace they had last week starts to leak away. I liked them more when they were smug and dangerous than when they were just loud.
Donna Out of Her Depth
The best material belongs to Donna, and it’s the first time this season has properly tested her. The Doctor gives her the key and tells her to wait in the TARDIS, which is exactly the sort of instruction she’s spent the whole run ignoring, and then the Sontarans teleport the TARDIS onto their ship with her still inside it. She’s alone, in the middle of an enemy warship, and visibly frightened. Catherine Tate plays the fear straight rather than for laughs, which is the correct choice.
It matters because Donna has spent her run being the person who tells the Doctor what to do rather than the person who does the running. Since the two of them put their hands on that lever together in The Fires of Pompeii, the show has been building her as an equal rather than a passenger, and this is where it starts cashing that in. She’s not clever like Martha or fearless like Rose. She’s an ordinary woman in a situation that’s far too big for her, and she holds it together anyway, which I think is better. Not everyone will agree, but I found it a lot more affecting than any of the shooting.
It also helps that the script trusts her. Den of Geek’s review from the week it aired picks her out as the one who keeps her head, and I’d say the same. Every time the plot threatens to turn into corridors and countdown clocks, it’s Donna’s reactions that pull it back to something human.
The Boy Who Wanted to Matter
The resolution is where the episode surprises. The Doctor builds an atmospheric converter to ignite the gas and burn the atmosphere clean, then heads for the Sontaran ship, not to use it but to offer them a way out first. Leave, or the whole thing burns. Staal, being a Sontaran, refuses without hesitating.
That offer is worth pausing on. He didn’t have to make it. He had the device built, the ship in range and every justification he could want, and he gave them a way out anyway, to a species that had just spent a day trying to suffocate a planet for breeding space. It’s the clearest statement yet of the line this Doctor keeps trying to hold: one chance, offered honestly, even to people who are obviously going to throw it back at him.
And then Luke Rattigan takes the Doctor’s place. The spoilt, insufferable teenager who sold his planet for a bit of flattery has watched the Sontarans make it very clear they were always going to use him and throw him away. So he teleports himself onto the ship, sends the Doctor back, and triggers the device. It’s genuinely affecting, mostly because the episode never asks us to like him. He doesn’t get a redemption speech, just a boy who finally understood what he’d done and made one correct decision at the last possible moment.
Meanwhile the Doctor was entirely prepared to die doing it. He’d told Donna and Martha to live good lives before he went, and nobody remarks on it afterwards, which is becoming a pattern worth watching.
What I keep coming back to is how little of this needed the Doctor to be clever. Most weeks he wins by spotting the one detail everyone missed. Here he wins by building a big machine, giving his enemy a fair warning, and then having a teenager take the decision out of his hands. It’s an oddly humble way to end a story, and I think it’s a big part of why the episode sticks with me more than the plot says it should.
Rating: 3/5. The most routine story of the run, heavy on corridors and countdown clocks, and the Sontarans lose a little menace once they’re just shouting at soldiers. But Donna’s night on the enemy ship and Rattigan’s ending lift it, and it never drags.
