Which you're very fond of. There have been too many detective novels set in universities and colleges. In my view, both Oxford and Cambridge have been rather overdone. The detective story has moved much closer to mainstream fiction. It no longer affirms with such confidence the probity of the state system, including the police.
Detectives are far less creatures of fantasy or romantic wish-fulfilment.
They tend to be professionals doing a difficult job in a modern world. One of the great virtues of the detective story in the 1930s was that it gave an extraordinary description of life as it was then. If you want to know what it was like to work in an advertising agency in London between the wars, then read Murder Must Advertise. As a novelist, she can't write with the others, but her achievement was absolutely astonishing. It may be easy to criticise her as a stylist, but she gave pleasure to millions of people.