Both of the books I'm recommending today are each, in their own ways, about cold cases.
After all, what could be colder than the mysteries surrounding the life of that pre-eminent Queen of Crime, Agatha Christie? Christie, by some calculations, is the second best-selling author of all time (beaten by a hair by Shakespeare). She was a resolutely private person and, so, has teased the legion of biographers who have been chipping away at her sphinxlike silence ever since she died in 1976.