I'm not sure if I should nominate a book I have read and loved, or one I want to read
So I'll pick one of each and people can decide to second/third/whatever if they want to.
1) Mistress of the Art of Death by Ariana Franklin (available at Fictionwise). Loved it. This was basically 'CSI set in 12th century Cambridge.' The main character is a female doctor who is essentially a coroner. She examines remains and tries to find out what happened to them. She is loaned by Rome (Italy has female doctors in the 12th century) to investigate a series of child murders in Cambridge. I read this earlier in the year and loved it. There is some early subterfuge where she tries to hide that it's her who is the doctor because England doesn't have woman doctors yet, but the core of the story is the mystery itself of who is the bad guy.
2) The Bicycle Shop Murders by Robert Burton Robinson. Downloaded this free from Feedbooks earlier in the year (it's not there now but it's 99 cents at Smashwords) and have not read it yet, but it looks interesting. The author synopsis says: Greg Tenorly lives a quiet and lonely life in a small East Texas town, until he is selected as a juror for a murder trial. A beautiful, mysterious redhead befriends him, and seems to have a romantic interest. But is she merely using him to influence the outcome of the trial? By the end of the first week, three people connected with the case are dead, and Greg is beginning to fear for his own life. He is now convinced that a powerful Dallas attorney is directing the murder spree in his little town. But why? He is determined to find out. But his investigation just might earn him a spot at the top of the hit list.