Enjoyable collection of murder mystery stories rehashed as fantasy tinged with an SF flavor -- which is how some of these stories managed to appeared in Bova's Analog. An alternate universe where King Richard ruled and eventually an Ango-French empire founded in magic settled in for the long haul. The first mystery, A Matter of Gravity (Analog 1974), while contrived, is the most clever. A locked room mystery where Lord Darcy early on announces he knows who did it but not why or how -- and that makes perfect sense at the end. The Ipswich Phial (Analog 1976) is more of a spy story with a rising Poland as the nemesis. An OK adventure but nothing that clever. I'm convinced that the The Sixteen Keys (Fantastic 1976) was meant to be printed with a floor plan. It's the weakest story with a resolution that is the kind of puzzle normally seen in one of those one-page Minute Mysteries. The Napoli Express (Asimov's 1979) announces its intentions up front. In terms of background it's a pretty direct sequel to the Sixteen Keys.

Recommended as lightweight entertainment. ( )

I concur with the general substance of the "reviews" below, and only add that I enjoy them tremendously everytime I reread them, possibly because I was a great fan of the "real" mystery writers that Garrett implicitly alludes to and borrows from.

At least two of the story titles are parodies of well-known thrillers or mysteries. (The Ipcress File & Murder on the Orient Express). See the Wiki "spoiler" for similar information.

Goodreads: Welcome to an alternate world where Richard the Lion-Heart did not die in the year 1199... where magic is a science and science is an art... where the great detective Lord Darcy and the sorcerer Sean O'Lochlainn combine occult skills and brilliant deductions to bring criminals to the King's Justice and thwart those who plot against the Realm. Welcome to a world where murder may be committed by magic most foul, but crime still does not pay - as long as Lord Darcy is on the case.

Wikipedia "Lord Darcy":... is a detective in an alternate history, created by Randall Garrett. The first stories were asserted to take place in the same year as they were published, but in a world with an alternate history that is different from our own and that is governed by the rules of magic rather than the rules of physics. Despite the magical trappings, the Lord Darcy stories play fair as whodunnits; magic is never used to "cheat" a solution, and indeed, the mundane explanation is often obscured by the leap to assume a magical cause.

Two more Lord Darcy novels, Ten Little Wizards (1988), and A Study in Sorcery (1989), were written by Garrett's friend Michael Kurland after Garrett's death.
The two titles were manifestly modeled on those of famous detective novels by, respectively, Agatha Christie and Arthur Conan Doyle. This is similar to the way that Too Many Magicians was modeled on a famous novel by Rex Stout (whose Nero Wolfe and Archie Goodwin have counterparts in the novel's universe in the Marquis de London and his Special Investigator, Lord Bontriomphe).
...
The strong relation between Lord Darcy and Master Sean O'Lochlainn in some ways recalls that between Dorothy L. Sayers's Lord Peter Wimsey and his servant Mervyn Bunter. In both cases there is a successful detection team composed of a nobleman and a commoner, with a built-in social hierarchy tempered by a strong and long-lasting personal friendship; in both cases, the commoner partner is an extremely capable and competent person, highly appreciated by his socially-superior noble partner; and in both cases, the partnership started as a wartime relationship between an officer and an NCO, and carried over into civilian life. Garrett's debt to Sayers and Lord Peter Wimsey perhaps strayed over the line in "A Matter Of Gravity" in which the method of murder was essentially a direct copy of the method in Sayers' "Busman's Honeymoon."

Wikipedia (2021-03-28)
Gordon Randall Phillip David Garrett (December 16, 1927 – December 31, 1987); pen names David Gordon, John Gordon, Darrel T. Langart, Alexander Blade, Richard Greer, Ivar Jorgensen, Clyde (T.) Mitchell, Leonard G. Spencer, S. M. Tenneshaw, Gerald Vance.

Goodreads added pseudonyms: Gordon Randall Garrett, Gordon Aghill, Grandal Barretton, Ralph Burke, Gordon Garrett, Blake MacKenzie, Jonathan Blake MacKenzie, Seaton Mckettrig, Mark Phillips (with Laurence Janifer), Robert Randall. ( )

(see copy 1) ( )

Great alternate reality fantasy. ( )

(see copy 1) ( )