Margery Allingham's The Crime at Black Dudley (1929) marks the introductory appearance of Albert Campion, who would feature in 18 future novels.
And quite an introduction it is:
"That's a lunatic.... His name is Albert Campion," she said. "He came down in Anne Edgeware's car, and the first thing he did when he was introduced to me was to show me a conjuring trick a two-headed penny -- he's quite inoffensive, just a silly ass."
Campion figures heavily in one plot thread -- involving a group of Bright Young Things being held captive in a country manor filled with secret passages -- but plays no role in the solution of a secondary murder mystery.
Those expecting a sedate country house locked room puzzle should look elsewhere. (The degree of seriousness with which The Crime at Black Dudley was written is indicated by the name of the villain: Eberhard von Faber!)
Phillip Youngman Carter, in his preface to the short-story collection The Allingham Casebook, says the early novels "reflect the mood of the time and into them she crammed every idea, every joke and every scrap of plot which we had gathered like magpies hoarded for a year."
Two daggers out of four.