After finishing The Second Deadly Sin, I came to the conclusion that most probably, for me, no book in the Rebecka Martinsson series will equal Sun Storm, the very first one.
I keep reading them because I grew attached to Rebecka and even more to Anna-Maria Mella, and I have a good time reading them, but they never totally grip me like Sun Storm or some other thrillers did/do.

This was particularly true in this case (and as a result, it took me forever to finish it) because I quite disliked the WW1 story. First, I'm totally over the alternating historical/contemporary narrations that are such a strong trend in crime novels those days and I can't wait for this to die down. Plus, here, I thought the historical story was pretty weak (can't say more because spoilers!).

But The Second Deadly Sin wasn't all bad, far from it. The opening scene with the bear was awesome (and probably got my hopes too high, lol), and the character of Marcus, as a little traumatized yet resilient boy was very well depicted, quite far from the usual tropes and clichés. I also really like Eriksson and was very pleased with the way his storyline went on.
And then, of course, there are all the details about how Kiruna came to exist, those were super interesting.

All in all, still a solid read but not a must-read IMHO.