This episode begins with the Doctor and Rose chasing some sort of metal thing that is hurtling towards earth. They land on earth in 1941, on the night of the London Blitz. They are trying to find this object, which is difficult when bombs are falling from the sky. Shortly after they land, Rose spots a small boy calling for his mummy. She calls to the Doctor to help her, but he was already inside. So, according to TV logic, she goes after the child wearing a gas mask all by her self. She gets carried off on a blimp, where she is saved by a rogue Time Agent, Captain Jack. With his help, Rose and the Doctor figure out what happened to the metal object and what it's doing to anybody who comes in contact with it--and how the small boy is involved. Episode 10 is simply a part two of episode 9.
While I realize that's a crap synopsis (I should just take them from IMDb), that is essentially what the episode is about. I liked the creepiness of this episode. Because the people in gas masks are essentially zombies who call out for their mommy (sorry, mummy) every few seconds. I also liked the mystery, and how they brought up little parts of the answer throughout the episode, and if you weren't paying close attention, you would miss them. Examples being: the little boy's seeming obsession with his older "sister," the little light thingy bots whose name escapes me...which I totally figured out were significant, FYI. I also liked the addition of Jack, though I thought they did the whole "We're attracted to each other" thing with him and Rose a bit too thick. It sort of became irritating after a while. In episode 10, I appreciated the sort of competition between Jack and the Doctor, which was entertaining. And I really liked (spoiler!) that moment when the Doctor and Rose were trapped in a room by the zombies, and Jack had left, and they were about to dance, but they were talking about Jack, and then it turned out that Jack had teleported them who knew how long ago, and they hadn't even noticed. I thought they did that really well.
And then of course, the Doctor legitimately dancing at the end, and getting the dance out of Rose even when Jack asked for it. I also appreciated their incorporation of the title of the show: Doctor Who. Rose was asking who she should say it was, and he said the Doctor, and she asked, but Doctor who? I've only seen half of the next episode, so I shall wait til I finish it to write about it. Later!
Mask Creatures: [with increasing intensity] Mummy, mummy, mummy, mummy, mummy, mummy, mummy, mummy, mummy, mummy.
The Doctor: Go to your room.
[mask creatures stop]
The Doctor: Go to your room! I mean it. I am very, very angry with you. I'm very, very cross. Go... To... Your... Room!
[mask creatures turn and go back to their beds]
The Doctor: [sighing] I'm really glad that worked. Those would have been terrible last words.
UPDATE: This is one of my favorite episodes of all time, despite it being in Season 1, easily the worst season. Even to this day, in season 6, I remember these episodes as two of my absolute favorites. I'm rewatching them, now, in fact. Just sayin'.