This event should have come with a ‘spoiler alert’.

Whilst everyone had surely read ‘The Suspicions of Mr Whicher’, a straw poll showed most of this audience hadn’t yet read Kate Summerscale’s new book ‘The Wicked Boy’, and many had just bought a hard-backed copy.

Yet it was half an hour in before Claire Armitstead, Guardian Books literary editor in discussion with Summerscale, sat up and suggested the last bit at least should be left to the reader. Relief at this better-late-than-never suggestion was audible.

This said Summerscale was generous in her account of her ‘enviable life’ immersed in research and making stories, scrupulously only out of facts uncovered in this case from contemporaneous newspaper reports, an Old Bailey criminal trial transcript, and sensational so-called Penny Dreadfuls, said to have influenced her latest Victorian protagonist.

Summerscale honed her meticulous respect for reported fact writing obituaries on The Daily Telegraph, a job which inspired her imagination and led to her first book ‘The Queen of Whale Cay’, but did not lend itself to artistic licence taken by, say writers of faction.

Armitstead described reading through piles of ordinary books in bed before - to some hoopla - ‘finding’ Mr Whicher which won the Samuel Johnson Prize for Non-Fiction in 2008.