Haven't seen it in a long time and remember very little, but here goes nothing. Also Ten and Donna decide to crash a gay tea party. There they meet Agatha Christie which results in them getting caught up in some wacky Christie-esque murder mystery. At one point the Doctor faces death as he is poisoned and salty salt is involved. Also Donna may have raped him. It's eventually revealed that the Priest is the killer, though I can't remember who he killed or why. Also I have a feeling he turned into a giant terrible CGI wasp for some reason, but hopefully that was just the cocaine talking.