3. Midnight
This episode is frightening. It sounds trivial enough to begin with; the Doctor and Donna visit a resort planet. Donna doesn't want to go with him on a trip to visit a waterfall made of sapphires, so he takes off on his own. But then the shuttle stops in the middle of the trip; there are these strange knocking noises outside on the hull of the ship. The noises seem to follow the passengers and end up where a passenger named Skye is cowering. It all sounds innocuous enough, but what is difficult to convey is the subtle building of tension that happens in this episode. Essentially, it's an episode where the Doctor is just talking with other people. That's it. And it ends up being terrifying. The unseen villain of the piece possesses Skye and uses her to repeat what the other passengers are saying. Then it zeroes in on the Doctor and starts to repeat him. You wouldn't think that just simply repeating what someone else says would be unnerving, but it totally is. The alien ends up possessing the Doctor; and Tennant's performance is fantastic. The fear he conveys at being taken over grips you and takes you to the edge of your seat. But the thing that really gets you is the other passengers and their fear. What would you do if you were in that situation? I would hope to be the voice of reason, but then there is a little part of me that would be all for throwing the threat out the door to save myself. It's an indictment of human nature which writer/show runner Russell T. Davies handles superbly. What is really scary is that they never explain what happened. Having the Doctor powerless is something that we rarely see. At the end of this episode he didn't solve the problem and never even knew the name of the alien that had possessed him. Frightening indeed!