In Biggers' final novel, Charlie Chan is invited to millionaire Dudley Ward's home in Lake Tahoe to try to find his missing son. However the murder of Dudley Ward's ex-wife, the soprano Ellen Landini, soon occupies his complete attention, and potential suspects abound. He examines the evidence but seems unable to persuade Ah Sing, the titular keeper of the keys, to break his loyal silence and give him the key to solving the mystery.