Ooooooh, fun! Doctor Who is all about time travel, yet rarely touches on the potential consequences of moving around in time and changing things. This episode does just that, and plays around with one of the oldest temporal paradoxes. You know the one: “what if you go back in time and kill your grandfather?” Only this time, it’s “what if you go back in time and save your father’s life?”. Well, the answer is (as you might expect) Very Bad Things.
Rose persuades the Doctor to take her back in time to the day her father (of whom she has no memory, other than what her mother has told her) was killed in a hit-and-run accident. Impulsively, she pushes him out of the way of the car, which seems like a good idea at the time.
But this action causes a rift in time, which lets in monstrous creatures known as Reapers, who proceed to kill anyone and everyone. The Doctor tells Rose that in the, err, past the Time Lords would have prevented the Reapers from destroying life on Earth, but now there’s nothing to stop them.
Then the Doctor is apparently killed by a Reaper that has managed to get into the church in which a small group are hiding. Is this the end? Well, obviously not, as there are more episodes to go . The true hero of the story turns out to be Rose’s father, who has realised that his survival was the cause of what is going on, and throws himself in front of the car that’s been appearing and disappearing all through the episode. The Reapers disappear, and the Doctor and the other “dead” people reappear. Time has been restored. Well, near enough, anyway…
Good stuff. More character development, and some fun and games with a younger version of Rose’s mother.
 Or become your own grandfather, but as Douglas Adams said, that’s something any well-adjusted family should be able to cope with
 Or become both your parents, as in a Robert Heinlein story, but I digress…
 Really nice CGI monsters, too
 Look, time travel gets confusing
 OK, there is a problem here. We know the Time Lords have all been killed in the Time War, but the implication is that they’ve been removed from time altogether, otherwise they’d still be around, or have been around, or, err, maybe I should stop thinking about this before I disappear into a timewarp of my own