The Doctor and Donna land on a planet that's a huge library. They wonder why nobody is there and when they ask a courtesy node, they find out that the library is locked. The node gives them a warning as well: "Count the shadows". Suddenly the lights go out and the Doctor and Donna run into a small shop with a sky light where they seem to be save from the shadows. Then other people arrive, which turn out to be archaeologists. With them is Professor River Song, who seems to know the Doctor but he doesn't know her. That is a bit of a shock for River but soon she has no time to think about it because the Doctor has found out what's hiding in the shadows. It's the Vashta Nerada, a small, flesh-eating alien race. They start to kill the members of the expedition and the Doctor tries to find a way out of the library. There is also the mystery of the little girl who thinks the library is a thing of her imagination and is really upset when suddenly people are in there. What will happen next?
I really like this episode although it's one of the scarier ones. It marks the first episode of River Song but at this time she's still a mystery to all of us. Alex Kingston plays her brilliantly and her interactions with David Tennant's Doctor are great as well. The Doctor doesn't know who she is but somehow he knows that he can trust her. It's so sad when Donna talks to the dead girl and tries to calm her down until the rest of her conciousness is gone. That's one of the saddest moments Donna is in. The Vashta Nerada are very scary aliens because you can't really see them and they can kill you in an instant. They've been in the library for such a long time already and they have learned to adapt to it and they are very hungry. This first episode of the two-parter is brilliantly written by Steven Moffat and you can just hope that everything will end in a good way.