When a dying man asks for Mr. Wong's help (played by Boris Karloff), this begins an investigation of his murder and that of two others. Spies and a formula for a poison gas are involved.

The first installment in the beloved Mr. Wong film series. Here, we are introduced to the Oxford-educated detective (played by Boris Karloff) and his unique crime-solving skills. When three businessmen trading in toxic chemicals are murdered, the suspects are many. But Mr. Wong picks up on a common thread that he believes will lead him to the real killer—and the true motive! Based on the Mr. Wong character originally created by pulp fiction writer Hugh Wiley.