4. Gervase Fen
Created by: Composer Robert Bruce Montgomery (he wrote the scores for the early Carry On films) under the nom de plume Edmund Crispin. Crispin wrote nine novels and two short story collections about Oxford don and amateur sleuth Gervase Fen from The Case of the Gilded Fly in 1944 to the posthumously published Fen Country in 1979. He is probably the last great writer of classic mysteries. In his own author biography he described his favourite pastimes as including: "excessive smoking, idleness, and cats", while expressing a strong disliking for: "psychologically realistic crime stories and dogs".
What's his appeal?: Doctor Who writer Gareth Roberts (one of his episodes was, naturally, the Agatha Christie one) described a Fen mystery as: "more like Doctor Who than Doctor Who". What this means is an egocentric eccentric dashing about all over the place, always seeming one step ahead of the audience even while narrating his thoughts as he makes them up. Unlike Berkeley, Crispin is uninterested in the psychologically plausible. His stories are created purely for the fun of it and are full of imaginative silliness and a fair bit of fourth wall breaking. It's this pace and sense of joy that would be great to see on screen.
Sidekicks and supporting cast: There are not really any recurring assistants in Fen's world. Each story is essentially standalone, which might make adaptations easier. He's usually wading in to help a fellow academic or writer, though, and a new supporting cast of colourful characters tends to get swept along with his enthusiastic mystery solving in each story, not always in a fashion that's pleasing to them.
Any on screen previous?: Aside from the Carry On films, Crispin's on screen legacy is almost identical to Berkeley's: an episode of the Detective anthology starring a Hammer regular and a loose Hitchcock adaptation. In the case of the former, Fen mystery The Moving Toyshop was the first episode in 1964 and featured Richard Wordsworth, who had had a bit part in The Quatermass Xperiment amongst other things, as the Oxford don. The Moving Toyshop's carousel based finale was also pinched for the climax of Hitchcock and Raymond Chandler's version of Patricia Highsmith's Strangers on a Train. The rest of the film, though, came from Highsmith so there was no Fen in it.
If they only made one: There's a reason why The Moving Toyshop is the Fen story already to have some screen pedigree. It stands out as the most thoroughly entertaining Crispin novel and could definitely use another screen outing. The bizarre plot is delightfully bonkers as poet Richard Cadogan discovers a dead body one night in a toy shop, only to return the next morning with the police to find not only no dead body, but also that the shop is a grocer. It turns out it's all part of a murder scheme related to an old woman whose money has been left to strangers referred to only through limericks.