Light novels written by the same author, both focus on murder mysteries with great writing that not only leaves you on the edge, it also has plot twist that you just didn't see coming. You might have though you've seen a plot twist coming, but it was actually plot twist of the plot twist. The author is always step ahead of the reader with the mind games and it's great.
A female police officer does the footwork for a reclusive and unusual genius detective, with their primary (or sole) method of communication being a cellphone. Aside from the similarity in setup, both are keen on 'fair play' mysteries -- you can indeed play along at home.