I started watching Castle earlier in the season after being hesitant toward picking it up, but some of the episodes are just average in my eyes, and this was one of them. A very loosely-thrown together plot here (a rich guy shows up dead, various suspects emerge) and the butler jokes got tiring after awhile. I felt as if Castle was trying to be too Tony DiNozzo in this episode, for those that get that reference. I did not like Beckett going under cover at the club either. Way, way too cliched in my mind to pull that.
Still, the ending did catch me a bit off guard here tonight, and overall it wasn't bad. Just not one of the better episodes of the season.