I recently read Swan Song by Edmund Crispin, one of his Gervase Fen mysteries. At one point a journalist asks Fen for an interview. She’s doing a series on famous detectives: “I’m hoping to do H.M., and Mrs. Bradley, and Albert Campion, and all sorts of famous people.”

I didn’t immediately recognize the first two names, but Albert Campion is Margery Allingham’s series detective, who in 1947, when Swan Song was published, was still appearing in new books. Google revealed that “H.M.” was John Dickson Carr’s Sir Henry Merrivale (which I should have known), and Mrs. Bradley starred in a nearly forgotten (but intriguing-sounding) series by a third author.

This was interesting. I’ve seen writers make use of public-domain characters, and I’ve seen covert in-joke references to their colleagues’ work. (For example, as I recall at least one of Randall Garrett’s Lord Darcy stories had characters obviously based on Nero Wolfe and Archie Goodwin.) I haven’t often seen a writer explicitly and unilaterally connect his own fictional universe with one created by another contemporary writer. In fact, I can think of hardly any. Two things come to mind: a Star Trek tie-in (Ishmael, by Barbara Hambly) which is apparently a crossover with an old TV show I’ve never seen, and a recent post on The Valve about a 19th century hack who tried to latch onto Charles Dickens’s coattail by taking his melodramatic trunk novel, slipping in a couple of cameos by Dickens’s Paul Dombey, and calling it Dombey and Daughter. (This kind of thing must have happened more often in the days of loosely-observed copyrights; it’s possible I’ve heard of, and forgotten, similar incidents from the period. Not that it’s a great example in any case; it’s a cynical appropriation by a hack. The line from the Crispin novel was friendlier, and came from an equal.)

If anyone comes across this post and knows of other examples, let me know in the comments.