The Affair of the Mysterious Letter

The Affair of the Mysterious Letter is a 2019 fantasy-detective novel by Alexis Hall. It was first published by Ace Books.

Synopsis
When injured physician Captain John Wyndham moves into the spare room at 221B Martyrs Walk in the multidimensional city of Khelathra-Ven, he soon finds himself recruited by his new roommate, consulting sorceress Shaharazad Haas, in a quest to discover who is blackmailing Haas's ex-lover Eirene Viola.

Reception
Publishers Weekly called it "zany queer and fantastical" and a "fun riff on canonical works of fantasy and detection" that "froths with magic and humor". The Chicago Review of Books lauded it as "an exciting romp through a truly imaginative universe (or, more accurately, multi-verse)", comparing Haas' cosmically aware nihilism to Rick Sanchez, and praising Hall's "wit and empathy", but also found that he too strongly emulated the prose of Arthur Conan Doyle in a way which was "enjoyable at first" but eventually "burdensome to the narrative."

James Nicoll considered it to be "hilarious", and noted its "ample LGBTQ+ representation", with "over-the-top unconventional" characters who are "queer as fuck".

Locus described it as "weird and witty", with Khelathra-Ven serving as a "fascinatingly warped" setting in which "the quirky characters hold the plot together," but nonetheless faulted it as "more a string of adventures than a cohesive mystery".