In Shanghai, Ralph Bonner agrees to deliver a dagger to Lee Fong in San Francisco. Afterward, several attempts are made to steal it from him, but he reaches the United States with the dagger intact. While Ralph and his brother Jim set off into the rainy night to deliver the dagger to Lee Fong, Mr. Varanoff, a crook, conspires with Madame Ying Su to steal the dagger for themselves. Lee Fong is delighted to see the dagger, but just as he reveals a secret jewel in the dagger's hilt, the lights suddenly go out. When they come back on, Lee Fong is dead, and Ralph and the dagger have disappeared. The police suspect Jim, but Lee Fong's white ward, Lotus, has fallen in love with him and defends him. Dissatisfied with the progress of the police, Jim decides to solve the murder himself. He contacts Madame Ying Su and discovers his brother is being held on the premises of her café. Lotus follows Jim to the café. To allay Ying Su's suspicions, Jim offers to question Lotus about the dagger. Instead, he secretly warns her that they are being watched and the two of them try to escape. Lotus manages to get away and arrives with the police just in time to save Jim from death at the hands of Ying Su. They rescue Ralph, who explains the mystery. At last, they discover the dagger where Lee Fong hid it before he died.