This is the 3rd in the Sherlock in Minnesota series. I have read (listened) to all 3. Millett has done a good job capturing the Sir Arthur Conan Doyle feel but throwing in some American flair.
Sherlock and John are called back to the great northern state of Minnesota when a representative of the King of Sweden stops in to ask for help with a Rune Stone. Once arriving they jump right into a murder scene. Lucky for them Shadwell Rafferty is back to help the m in one of the hardest cases of their careers. Sherlock is sure the Rune Stone is a fake, but being as everyone who seems to know where the stone is kept turning up dead and they have a tough time tracking it down.