Robert Keable apparently wrote Simon called Peter in twelve days – that's two chapters a day – when he went back to missionary work in Bechuanaland after the war. I learnt that from Hugh Cecil's chapter on Keable in The Flower of Battle (The ODNB is predictably silent about him, despite finding room for hundreds of bishops who had far less public impact.)
As one might have guessed, Simon called Peter is sort-of-autobiographical, except that Keable's own private life was a bit messier. He was a missionary in Zanzibar, came back to England in 1915, went back to Africa – Bechuanaland this time (These days it's called Botswana, and Precious Ramotswe lives there). He and his wife were apparently “sexually incompatible”, so when he accompanied African troops to France as chaplain, he found a few temptations, notably “Jolie”, on whom the Julie of his books is based. His wife was a Catholic and wouldn't divorce him, so things got awkward.
My description of the book a couple of days ago probably made it sound like total tosh. Sex-as-sacrament gets silly enough when D.H.Lawrence does it, and Keable, speed-writing and spurting his desire all over the page, isn't in the same class. What's interesting about the book is the background, the description of officers with their Kirschner pin-ups and their whisky, and their liaisons with French girls. This is a war novel with no fighting – just one air-raid to remind us that nasty things were happening. The book is set in the dock area of Le Havre, and among labour units of the army, cutting down trees and so on.
So while it belongs to a standard genre – man goes to war and discovers the realities of life – his discoveries aren't the usual ones, but all about sex, which must have been quite exciting for readers in 1921. Simon Called Peter sold 300,000 copies over the next six years. Its success probably comes from the standard secret of a best seller – saying what your readers want to hear, but saying it with conviction, because that's what you believe, too. The book is both artless and cleverly written. The sexual theme is introduced gradually. We begin in the sedate atmosphere of the social novel, go to war, and gradually get more and more involved in sexual matters, till the final chapters are a climax of excitement:
Peter caught her to him. He crushed her so that she caught her breath with the pain of it, and he wound his hand all but savagely in her hair…