While pilots are meant to introduce comcepts and characters, second episodes are supposed to get people hooked. This episode certainly did just that. The manifestation of OCD was hidden throughout the episode, but so obvious when explained - just what a mystery should be like. Acting's not excellent yet, but we all know they get there in the end.
The subplot with Gideon was a little confusing - I couldn't tell where it occured in the plotline when you take into account what he was teaching that class previous episode. But I liked it all the same.