Aliens hiding in plain sight isn’t an unusual concept to the Doctor. Many species have the ability to conceal themselves from discovery, either by being able to change shape or colour and thereby blend into the background, or through camouflage technology and the bending of light rays. Perception filters work along similar lines, allowing something or someone to be right out in the open and yet completely ignored by most people. A few are able to see past the filter, but the ability is rare enough not to be worth considering.
This is different though; these aliens are actively disguising themselves as humans, and they’re up to no good.
An unknown number of aliens are wearing the skins of humans as if they were nothing more than suits of clothes; that’s bad news. The Slitheen family are obviously not the nicest of people, and they’ve wormed their way into the highest levels of British government, simply by taking people’s skins. Wear the skin, and be the person.
It shouldn’t work so well, and yet it obviously is. Despite the aliens having an unfortunate tendency towards childish body humour, no one seems to notice any difference. As far as anybody who knows them is concerned, they’re the same people they’ve always been. Nobody has any idea their colleague, or friend, or family member has had their stuffing replaced, as it were. So they’re a bit on the gassy side, so what? Politicians have always been full of hot air.
In some respects it’s an ingenious method of disguising oneself, except that it makes every member of the Slitheen family a murderer.
Individual murders are small fry compared to what the family have planned though; they intend to start a war and reduce the earth to nuclear rubble, then get rich by selling it off as starship fuel. Never mind that earth doesn’t belong to them and happens to be inhabited. All they’re concerned with is their own greed.
Still, the Doctor isn’t about to let this bunch destroy one of his favourite planets, especially not while he’s on it, and because he’s brilliant, he has a plan. All he needs is for a missile to be fired at Downing Street, where the Slitheen are trapped. It’s unfortunate that he and Rose are in there too, but you can’t have everything. Of course, it also means someone else has got to aim and fire the missile, putting the safety of the entire planet squarely in the hands of Mickey the idiot.
They’re only going to have one shot at this. All the Doctor can do now is hope that Mickey doesn’t miss. That would be beyond embarrassing.