I don’t like the word “whodunit” very much. It is a restrictive term that explains nothing. This word was coined around 1935 by Wolfe Kaufman and it pointed out the importance of “who-done-it” in the mystery fiction, the identity of the murder, reducing the detective stories as “mere puzzles”.
In the mystery fiction between World War I and World War II, when the Golden Age is usually delimitated, there was a real emphasis on plot, clues, thinking and puzzle, but they were virtues, not defects.
The term "whodunit", actually, doesn’t explain the real essence of Golden Age mystery: the power of ingenuity, the purpose of the writers to surprise the readers, with complex plots, bizarre problems, eccentric characters and unexpected solutions.
Many of the best-known writers of so-called whodunits were British - Agatha Christie, Anthony Berkeley, Dorothy L. Sayers, Michael Innes - but there were some great American authors that in few years revolutionized the genre: S.S. Van Dine and his followers, like Ellery Queen, Anthony Abbot, Charles D. King, and other masters like John Dickson Carr, Rex Stout and Clayton Rawson. The real question to pose in their novels is: howdunit? Locked room murders, people, houses, things that vanish into thin air and other impossible events: this is the Golden Age mystery.
If we analyze the works of these authors, we could conclude that there is much more than simple “who-done-it” in their books: most of the Golden Age writers were brilliant highbrows and talented writers. As the great Igor Longo said years ago, speaking of ingenuity, plot and misdirection, even the third-class mystery Golden Age novels, if confronted with crime stories of nowadays, would win hands down.