This is a rather odd episode, as three distinct plots develop side by side with very little interaction. Paige is barely here at all, although you can already feel that being Mrs Wife isn't enough for her. Phoebe is busy reviewing her love life with Coop, and although it is well done, the final lesson (falling out of love sucks, but what matters is falling in love) is not too deep, and doesn't reveal anything about Phoebe or the story. Its main purpose, apparently, is to bring Coop and Phoebe together. Piper's plot is more complex, as she has to fill in for her husband and find how to vanquish two unvanquishable demons. Really, even though they are demons, I find Leo's teaching methods rather disturbing, but as he's currently in deep-freeze, let us skip that. That plot is clever and it works, because it goes somewhere. Piper learns that she can manage on her own, and that Leo is still with her, speaking through Wyatt's adorable piping voice. We also find out what became of the students after the school went to hell (literally), and how useful that school was to the magical community: those two teenagers may not look like much, but they can really kick butt.
Finally, Christy and Billy are at the core of the main plot, since Christy is trying to win Billie over to her side. As previously, what makes this interesting is that the characters are not black and white: for all her misguided beliefs, Christy is a decent person who loves her parents and wants to do good... but she's also capable of the most barbaric violence, as shown at the end. The brutal murder of the girls' parents is a very good move. It would have been different if this was their first appearance, but now we like them, they have a back story and a personality(by the way, I notice that they have adopted a style halfway between their former restrained selves and their wild assassin looks), so we can only react more strongly to their death. Besides, it is bound to have a major repercussion on Billie and Christy, thus speeding the main arc up a lot.
Finally, Christy and Billy are at the core of the main plot, since Christy is trying to win Billie over to her side. As previously, what makes this interesting is that the characters are not black and white: for all her misguided beliefs, Christy is a decent person who loves her parents and wants to do good... but she's also capable of the most barbaric violence, as shown at the end. The brutal murder of the girls' parents is a very good move. It would have been different if this was their first appearance, but now we like them, they have a back story and a personality(by the way, I notice that they have adopted a style halfway between their former restrained selves and their wild assassin looks), so we can only react more strongly to their death. Besides, it is bound to have a major repercussion on Billie and Christy, thus speeding the main arc up a lot.