I originally posted the review below on 15 September 2019, but I've just realised I posted it on the wrong place in this site (against an edition that incorporates another short story, that I haven't read). D'oh! I've copied my 2019 review below.
A short story that I listened to on audiobook. The audio version lasts for only 27 minutes.
I normally think of Conan Doyle as a Victorian writer, but this story was published in 1929, a year before his death. It’s the last in the “Professor Challenger” series. Of those I had only previously read one, that being The Lost World, in which he first appeared. Challenger is as irascible and pugnacious as he was in that earlier book, and like The Lost World, this story also features the journalist Malone.
This one features a Latvian scientist, living in London, who invents a machine capable of destroying anything within its sphere of operation.
Average story, corny ending.