The Absent One (Department Q #2) by Jussi Adler-Olsen (Spanish: Los chicos que cayeron en la trampa)
I don't know if it was because I had longed to go back to reading or what, but I LOVED this book! It wasn't as mysterious as the first one, but what it lacked in suspense, it had in all the small details that make a great book.
The second installment of the Department Q series brings us together once more with Carl and Assad, but this time we see a more evolved relationship and a better work dynamic, so it's even more interesting than the first one. On this occasion, everything starts after an unknown person leaves a folder with a murder case that has already been solved years ago. Something doesn't add up, so Assad decides to convice Carl to look into it, and into a series of murders and assaults that have been unreported or unsolved and that may point to the same group of people that could be behind the first murder.
Although they show you early on who is really behind everything, this doesn't diminish the reader's interest in continuing with the book, and although for a moment I thought the ending was too predictable, it has twists that still surprised me.