Secret on the Thirteenth Floor
by Gertrude Chandler Warner
Black cats? Broken mirrors? The number thirteen? The owner of the art deco apartment building in nearby Silver City believes in all kinds of superstitions. The Aldens aren't so sure about most of them, but there's one thing they do know: something strange is going on on the thirteenth floor. Are they just coincidences, or is the building manager onto something?