The school's festival continued. We saw more of the somewhat depressed Mayaka, who had a squabble about manga with an annoying upperclasswoman from the manga club. At the end of the episode a very funny and awkward thing occurred. Chitanda realized that Houtarou saw some pictures of her cosplaying (taken at a festival's booth) without permission.
There is not much to analyze. Episode 13 of Hyouka was strong because we continued to see other aspects from the main characters' personalities. I am very glad the creators of the series opted out from introducing a new mystery. I give this episode a 8 out of 10.