It's Christmas!! Play, okay, it's actually the middle of May but bear with me, as it's Christmas in the world of K-ON! at least.
After being treated to a small flashback segment of Yui and Ui's childhood (complete with a rather "unique" white Christmas engineered by the former), it's time for the light music club to down instruments and prepare for their own Christmas party. Tsumugi's place is "booked" for the day, so it ends up being left up to Yui to provide the entertainment... Good job she has a reliable sister.
So, the day of the part rolls around, and somehow Sawako manages to gate-crash the event, bringing an "interesting" atmosphere to proceedings from her choice of present for the gift exchange down to her arranging of a scarily depressing version of pass the parcel. Funnily enough, it's largely Sawako that brings this episode up from the depths of mediocrity, providing more amusing moments than the rest of the cast combined.
Perhaps it's just difficult to get into the Christmas spirit in May, but this was probably one of the weaker episodes of this series thus far, saved only by Sawako's appearance as I mentioned earlier. Still, you can't really deny how adorable the Yui-Ui sibling relationship is played here, and the show's sense of fun still remains throughout out, so if nothing else we can consider that some more checkboxes in the moe database ticked off before hopefully returning to the musical side of things just a little next time around.