Ngaio Marsh 
Scales of Justice [EPUB ebook] 

A brutal murder with a golf club and an ingenious plot bursting with snobbery, suspicion , adultery and secrets — to say nothing of the dreadful crime of catricide…The lives of the inhabitants of Swevenings are disrupted only by a fierce competition to catch the Old Un, a monster trout known to dwell in a beautiful stream which winds past their homes.Then one of their small community is found brutally murdered; beside him is the freshly killed trout. Both died by violence — but Chief Detective Inspector Roderick Alleyn’s murder investigation seems to be much more interested in the fish…