Finite mathematics for business and the social and life sciences Book

The Case of the Constant Suicides (Dr. Gideon Fell, #13) by John Dickson Carr.

Distant cousins of the Campbell clan have been invited to the Shira Castle in the Scottish Highlands to attend a family gathering of sorts. It appears Angus Campbell has committed suicide. Then again was it murder. A desperately needed inheritance is at stake for the remaining family-Colin Campbell and Angus's former mistress.
The rather humorous way those distant cousins meet brings a lightheartedness to the story. Dr. Gideon Fell isn't on the scene until well towards chapter 9. His presence brings with it another dimension to solving this mystery.
This was one of the most brilliantly written mysteries (and a locked room mystery at that) in the Dr. Fell books. I was glued to the pages. Dr. Fell was a master investigator.