I also enjoyed the many references to other crime authors and their works. You’ll find Donald Westlake (and his alias Richard Stark) and Elmore Leonard, among others. These Easter eggs add to the fun, making this a sort of meta hitman story.
It is also nice to root for the main character. Some hard-hitting crime stories have “heroes” devoid of any likable attributes. But I found myself liking Sangster as he tries his hardest to do the right thing.
The bottom line is Upon My Soul is an easily consumable novel that will leave you wanting more, even though this story works as a standalone. Thankfully, there are two more books in the series, both of which I will be reading. Highly recommended.