Thought it was pretty dark and then watched Farscape and saw that it really wasn't. It's the one where Scorpius's back story is revealled and everyone is angry and pyscho. And Braca kicks ass.
Here be warnings: There will be spoilers, not only for the entire Potter series, but also for a Dance to the Music of Time, and there'll be references to Brideshead Revisted, and a good chance of me going off on tangents.