I quite liked that this was a different look at relationships than in the other Lanyon books (I've read so far). We start with Daniel and Sean already being in a relationship and one that they somewhat rushed into. That does result in some trouble (which tie in with the plot) and I think it's described quite realistically (up until the very end, more in a moment).
However...the mystery plot is rather thin. If you have read more than two crime novels you will be able to predict most of it. And the ending felt rather rushed, both for the mystery and the romance plot. Especially for the romance plot. It felt like Lanyon had originally intended to go for an open end with sequel-hook but then suddenly changed his mind and went for a HEA so it seemed like some major problems just vanished into thin air.
I think that could have worked great as a novel with more time spent on the development of the relationship and also a bit more on the crime-plot but as novella it's just too rushed.