The Secret Circle is still in its growing stages, trying to figure out what it wants to be, but "Heather" is a step in the right direction. While the previous episodes looked broadly at magic and the characters, this week's episode gives us a specific reason why the magic they harness is dangerous and some threats out there. It also helps that Heather is a scary adversary, able to jump up staircases.
I'm don't really prefer any combination of characters yet, but Cassie and Faye works well, better than Cassie and Adam at least. They do the spell on Heather to revive her, only for Heather, in demon mode, to go after them. Again, the villain is vanquished by the end of the episode, hit by a car. However, we do get a big plot moving forward, the demon snakes crawling into Melissa.
Interestingly, this was, I believe, the first episode without any of the adults. The show seems to work better without the adults, allowing for a more streamlined, focused plot. But the adults are crucial to the central mystery of the show, so it's doubtful there will be many more episodes like this.