I ran across this author accidentally. I enjoyed his post on a Goodreads group, pulled up his profile and was intrigued by descriptions of his works. I'm always looking for fun reads involving "bad" guys and assassins fits that category nicely. Block's Keller series sets the standard, of course, and Halm ranks right up there.
Katla, or LKE Enterprises as she calls herself, specializes in killing targets in a such way that they look accidental or natural. Coming up with credible scenarios necessarily challenges the authors and this locked-room novella (available for free for your Kindle from Amazon) is certainly as good as anything Carr might have come up with. I like the way Halm integrated some of the newer technologies into the plot. A good story and enjoyable way to spend time while waiting for something.
My only caveat is that, unlike Keller and Dot who go to great lengths to conceal their identity, Katla meets directly with prospective clients. That would seem to make her quite vulnerable if things blow up. Nevertheless, I intend to read all Halm's books. They have the added benefit of being set in Amsterdam, a great city. I did tire of the word anthracite in this story, however. I highly recommend Microchip Murder: A Katla KillFile (in that one the word bascule was perhaps overused. :) )
Halm's short novellas are published as part of a mini series called the Katla Killfiles. Get them.