A Very D Christmas (Zero at the Bone, #1.4)
Really well done story that both adds to the series and does a really good job of talking about bullying, especially gay-bashing. I question that this is really number 1.4 in the series because the last two short stories were leading up to something involving D being gone. I think this is probably 1.15. Anyway, it's standalone enough. Some stuff won't make sense but it's explained well enough that reading the other stuff isn't necessary. It does, however, contain spoilers for the novel and the first short story.