Where's the rest?

Jagger has been a thought of mine since the last book when we meet him at his bar, he is almost as gruff as Sheppard. Almost.
Rex is the go getter, or a runner?

While this was a really good story, characters fit well, the whole vibe was there from the previous books but this one left me hanging on more of the backstory for both of these characters.

Jagger and Rex are almost a grumpy/sunshine but not quite there.
Jagger pushes and Rex retreats, but why??

There was a lot left unsaid for these two as far as why they are the way they are and also that quick abrupt twist then that's it. I know these are short books but just a tad more detail would be great for these characters that could have more of their backstory on the page to add to the story.