Bloodhounds/Diamond Dust Omnibus by Peter Lovesey

Two enthralling mysteries featuring the irascible detective Peter Diamond.
BLOODHOUNDS: The Bloodhounds of Bath is a society that meets to discuss crime novels, but to their latest recruit they are simply a gaggle of dotty misfits. Until one of them reveals he is in possession of an immensely valuable stamp, recently stolen from the Postal Museum. Then the theft is overtaken by murder when one of the members is found dead in a locked houseboat, with the only key in the possession of a man with a perfect alibi. Enter Peter Diamond, head of the murder squad in Bath, and the beginning of a crime puzzle which would tax the brain of Inspector Morse.
DIAMOND DUST: A detective learns to suppress his feelings when a verdict is announced, and Peter Diamond reveals no joy when Jake Carpenter is sentenced to life imprisonment for murder. But the next day, when a women is shot dead in the Royal Victoria Park, Diamond’s self-control dissolves in an instant. The dead woman is his own wife. Barred from taking part in the investigation, Diamond begins a parallel one of his own – with very different results to those of his erstwhile colleagues.