The Last National Service Man by Reginald Hill

Tankie Trotter is the last National Service man. He never liked the idea of being conscripted, and he showed it in none too subtle ways. But time spent in the glasshouse doesn't count towards his two years' service, so here he is, several years later, with a grudge against anyone who can be blamed for having a hand in this wasting of long years of his life. Chief among them is one Andrew Dalziel, brash Chief Inspector in the Midyorkshire Police, who kept handing Tankie back to the army when he went AWOL.

If Dalziel had to be taken hostage, it's a fair bet he wouldn't have chosen to be accompanied by newly arrived, wet behind the ears university graduate DC Peter Pascoe, who isn't even a Yorkshireman. These things rarely come down to choice though, and their loss is our gain as we watch the first hours of a lasting partnership that seems like it can't possibly get off the ground.

I'm not sure this 1994 novella is still available (I picked it up second-hand) but anyone who has enjoyed Dalziel and Pascoe would be well-advised to seek out a copy. It's not a conventional mystery or detective story but it does involve crime and psychology and is by turns (or at the same time, in places) tense and amusing. Beyond that, it's a wonderful character study of colleagues who might not be as mismatched as either of them thinks at first.