I do love this episode and it covers a lot, so I'm going to try and be brief.
We start with that scene with which we are now familiar: Echo (while still Caroline) and Adelle sitting across from each other with that ubiquitous pot of tea between them, the papers not yet signed. We learn that Echo was caught in the middle of doing something against Rossum that she thought was 'right' and that Caroline and DeWitt have been circling around this for two years.
The Rossum Corporation, besides running the Dollhouses, do a lot of drug research. A vial of a new drug that they're testing (I can't remember what it does; A-level chemistry was enough for me) worth millions has gone missing and one student died by banging his head repeatedly against a window after ingesting too much of it. Rossum aren't requesting just one active - they need an army (dramatic, huh?)
Adelle gives the go-ahead because she strongly believes in the work that Rossum is doing and black vans swarm the campus - minus Echo who is on another engagement. It quickly becomes clear that the drug is spreading faster than the actives can round up the victims and faster than Topher can find an antidote.
Briefly in other news: Mellie asks that Paul forgets about Caroline and the Dollhouse after she was almost killed in the previous episode. Paul couldn't say yes or make a promise and Mellie walks out. The spoiler that I didn't mention in my last post: Mellie is a doll - what the Dollhouse calls a sleeper which is pretty self-explanatory. She managed to kill the assassin when her 'trigger' was invoked but then made her normal again afterwards. We see Mellie later at the Dollhouse where she's getting a 'check-up'. I'll get back to this later.
Whilst on her engagement, Echo sees a news report about the student who killed himself and feels an overpowering urge to get to Rossum and save 'him',. though she's a little hazy about who 'he' is, why she needs to save him and why she's feeling these urges. Echo is getting echoes of her life as Caroline and we see flashbacks of her in a relationship with a guy called Leo and they appear clearly devoted to each other. We've not seen anything of Caroline's life apart from the video sent to Paul and her talks with Adelle, and this episode reveals that Caroline was a fierce demonstrator and protector of animal rights, amongst other things. Ironic, really.
We slowly see others become 'infected': Mr Dominic, Boyd and then Topher and Adelle to a lesser degree. Adelle provides a brilliant description of herself while she's still lucid: "Sarcastic? Unfeeling? British? ... you have to admit, I am very British" and it's pretty awesome to see her lose this cool British demeanour with her hair flying everywhere while she eats her way through Topher's "drawer of inappropriate starches" and bounces on his trampoline. At least, I didn't see it, but I assume it was a trampoline. I love Topher and Adelle together.
Topher had assumed that the dolls would be immune to this drug - something about dolls lacking the thing in their brain that the drug affects - but slowly, all the dolls start getting affected with flashbacks from scenes in their past lives which their brain shouldn't have access to. We see that Caroline had drawn up an elaborate plan to break into the Rossum labs to film the animals being used for testing and these are the images that Echo is getting and what pulls her to the campus when she has no business there. Caroline did break in with Leo, only they got caught and her name was referred to Adelle as a potential candidate for doll-ship.
To sum up, because I'm not really sure that much of this post makes sense unless you've actually seen the episode: we learn shit-loads about Caroline and how she ended up in the Dollhouse. The drug affected dolls differently from humans: while humans just went a little crazy in a bring-on-the-straight-jacket kind of way, the dolls got flashbacks which is where we learned about Caroline and got an interesting glimpse into Victor's previous life. Mellie packs her bags and leaves her apartment and Paul doesn't seem too fussed; the bastard. Lots of other interesting things happen that will be explored in later episodes so I won't go into now.
As a final note, I still don't know how the drug was spread. I'm pretty sure that I didn't just miss it, because I can't believe that they would say it and it just went over my head. Topher touched on something about it being airborne or spread through touch, but Echo inhaled a concentrated dose rather than just in the air. And how the hell did it get to the Dollhouse to affect Topher, Adelle and Mellie? So confused. Anyone want to shed some light for me?