When Watts and Mycroft go for their regular Thursday night visit to see Homeless Dave, they are shocked to discover their friend is dead and his dog has vanished. The police write it off as a attack on a defenseless man and are not prepared to investigate any deeper into the case, but Mycroft and Watts think otherwise.
The thing I liked best about this story is that I didn't figure it out until almost the end, and that's why students are going to like it as well. There are some aspects that they just won't anticipate. Jolly good.