A fair few of the characters are from the Big Finish audio plays (Erimem, Hex, Bernice, Evelyn and Frobisher). Important and main points to note if you are not familiar with them: Evelyn travelled with Six and is a middle-aged history professor who makes wonderful chocolate cake, Bernice travelled with Seven and Ace and is an archeologist from the future who likes her alcohol, Hex also travelled with Seven and Ace and is a nurse from the near future, Erimem travelled with Five and Peri and is the daughter of an Egyptian pharoah, and Frobisher travelled with Six and is a mesomorph in the shape of a four-foot penguin. That should clear up any character-related misunderstandings (and perhaps sow incentive for more Big Finish devotees ::evil cackle::). The rest is dialogue, and is explained in the handy break-down below.

First set of dialogue snippets:
1) Ian/Barbara walked in on by One,
2) Ben/Polly by Two,
3) Brig/Benton by Three,
4) Tegan/Nyssa by Five,
5) Peri/Erimem by Five
6) Ace/Hex by Seven.

Second set: Same pairings in the same order approaching the Doctor some time after the incident and either apologising embarrassedly, ensuring his discretion or yelling at him about it.

Third set: Role reversal.
1) Polly and Ben walk in on Two/Jamie (Ben is unaware, Polly has trouble looking away ::grins::).
2) Two/Jamie walked in on by Victoria, who's suitably shocked and runs away.
3) Two/Jamie walked in on by an inquisitive and naughty-minded Zoe, whom they invite to join in.
4) Four/Romana II walked in on by Adric (accompanied by K9), who seems kinda naive about the whole situation.
5) Tegan walks in on Five/Turlough (Turlough is undeterred, while Five tries to shoo her away asap).

Fourth set: Jack :oD
1) Seven walks in on Jack/Bernice in the kitchen, probably not doing much but there's alcohol and most likely various states of undressedness :o)
2) Four is unsurprised by morning-after!Jack/Harry - Sarah's not quite so unruffled, and Harry's very embarrassed and very nekkid, but it's alright cos there's blankets.
3) Six walks in on Jack/Evelyn doing... something with chocolate cake - you don't want to know what, and neither do I :oD
4) Jack/Liz behind closed doors in the lab, Benton stands outside and advises Three not to go in :o)
5) Leela defends her right to sleep with Jack against Four's huffy protestations.
6) One walks in on Jack/Steven, and meets Jack for the very first time.
7) Six and Frobisher discuss Jack after he's gone - Frobisher is unaware of the term 'TMI' :oD

Here's hoping the story makes more sense to you now, and thank you for reading. Reviews make me very happy :o)