The house without a key - Earl Derr Biggers

John Quincy Winterslip, a young lawyer from Boston, travels to Hawaii to visit his wealthy uncle, Dan Winterslip. John had failed a request to retrieve and destroy a certain box from his uncle's house in San Francisco - but others are also eager to find it. He arrives in Hawaii and learns that his uncle has been murdered. When Charlie Chan offers to help solve the killing and the mysteries surrounding the box, the detective's main clue is a wristwatch with an obliterated number 2...whilst John, much interested in the chief suspect's daughter, assists Chan in solving the mystery.