Detective James Lee Wong is invited to a party by his wealthy friend, Brandon Edwards. A collector of rare gems, Edwards show him his most recent acquisition, a Chinese sapphire called "The Eye of the Daughter of the Moon." Although proud of his possession, the millionaire is filled with foreboding: he confides to Wong that he has received a threat on his life. That afternoon, Edwards is shot dead and the gem is stolen. Feeling a sense of duty toward his friend, Wong begins to investigate the murder with Captain Street of the police.