This is GOSICK!'s OP, and I really want the song haha.
In the 4th episode, we meet a new character, Avril, who seems to be a villian who just hasn't been caught yet. Victorique solves 2 mysteries flawlessly and without effort, and she's still a mystery to us, but it seems like they're going to start revealing stuff about her soon. She's just so gosh darn cute, and not in a moe way, but more of a innocent way.
Now go and watch it, because it's such a good anime!