Murdered on Halloween by Daisy Landish
This is a short read at only 50 pages, so not much time to develop the characters or plot. Jane and Kennedy attend a fancy Halloween party and someone wearing a similar costume to Kennedy is killed. Kennedy is later attacked and realizes who the culprit is.
My main complaint is that I wanted it to be longer. I wanted to get to know Jane and Kennedy better and have an actual mystery rather than Kennedy just recognizing them. Also, while it was set in London, its language is very American....