A long running mystery series about an investment banker / amateur detective, written by Emma Lathen (a pseudonym for co-authors Mary Jane Latsis and Martha Hennisart). The series includes examples of: * Always Murder: Whatever irregularities the business of the book has, it produces a corpse at some point. * Amateur Sleuth: Thatcher must solve the mystery before the Sloan can move on. * Author Existence Failure: The death of Latsis in 1997 brought both the partnership and the series to an end. * Comic Book Time: Thatcher is "a youthful sixty" in all books, from 1961 to 1997. * Eureka Moment: Once per novel. * Fair Play Whodunnit: The reader might not have all the solid evidence until after the fact, but does have all the clues that tipped Thatcher off. * Mystery