I've always been a secret locked-room fanatic. I read my first one when I was about ten or 11, Agatha Christie's 'Murder on the Orient Express,' with David Niven and Peter Ustinov on the cover.
The first proper mystery novel that I read was 'Murder On the Orient Express' with a gaunt David Niven and a cherubic Peter Ustinov on the cover. 'Orient Express,' you'll recall, is the one where everyone did it, which delighted me no end, and I was immediately hooked.