9 Best 9th Doctor Episodes

One trick that this this season loves to pull, which would be adopted and expanded upon by later seasons, is that The Doctor's dark side often leaves him sailing similar waters as his enemies. And one of the best examples of this comes from the episode Boom Town.

Somehow, one remaining member of the Slitheen from the aforementioned Aliens in London/World War Three survived the missile blast that killed her brothers, and has set up shop elsewhere. The Doctor has to find a way to convince her to tell him how to reverse her evil plan, which of course makes for some delightfully disturbing conversations between these two admitted killers.

You could argue that The Doctor was in a war when he took lives, so his actions are a good bit more justified than the Slitheen's. The problem is that The Doctor doesn't see it that way, and his adversary is aware of this. Making their relationship in this episode a fascinating back and forth between two people with very different approaches to the blood on their hands.