Another investigation for Honolulu detective Charlie Chan (Warner Oland). The Chinese government calls Charlie to Shanghai to investigate a murder involving an opium ring. However before he reaches port in Shanghai he receives a note warning him not to disembark, or else. Not detered Charlie continues his investigation even after multiple attacks on his life. After trying to capture Charlie the gang finally comes face to face with him and his 'number one son' in a shoot out at a murky Shanghai dockside.