I enjoyed the mystery very much but I found myself distracted by the historical errors and the constant back stories of every single character who comes into contact with Charles Lenox.
I prefer to have bits and pieces a character's history with the main character revealed as it relates to the story instead of dumping several paragraphs at time without them being relevant to what's currently going on.
For instance on page 121:
With this report, Graham's role in the case was at all probability at an end, and both men knew that Graham would thereafter resume his normal functions, but perhaps it is appropriate, nevertheless, to explain the reaction between the butler and his employer...
Followed by a 2 page back story that the author admits to being unnecessary. Since Graham is a major character it normally wouldn't bother me too much except by the time you get to it it's the fourth unnecessary back story you've had to read.
Fast forward to Pages 261-262 and you have the back story of a very minor character, Mr. Throckmortin. In fact, these are the only pages you can find him. But this time there is also a glimpse into the future:
Perhaps it is worth relating that the next day, though busy, Lenox remembered his young friend and sent his mother two fine legs of lamb and a case of his own favorite port for Mr. Throckmortin, Sr. And though it would take many years, the clerk's final words were prescient, for he would help Lenox in the case of the Queen's amulet...
After this you're quickly brought back to the present and continue to follow Lenox through the rest of the day. Very distracting and takes away from the story.