It is noteworthy among adventure serials as containing an unusually high number of fistfights, all staged by director William Witney and a team of stuntmen.

It also sees the return of Witney's wife, Maxine Doyle, to acting for the first time since they met on the set of an earlier serial, S O S Coast Guard (1937).

After Japanese spies from the Black Dragon Society infiltrate United States borders, Federal Agent Rex Bennett is enlisted by the government to capture them.

As Oyama Haruchi, leader of the dangerous paramilitary group, begins to destabilize the United States war effort through sabotage and corruption, Bennett must team up with British special agent Vivian Marsh and Chinese special agent Chang Sing to stop them and help win the war.

The Black Dragon was commissioned based on the success of the serial Spy Smasher, although the production team preferred to have a non-costumed character.

This arrangement almost led to slight trouble in the relationship when Australian actress Constance Worth turned up at Witney's hotel room drunk.

It became an unofficial sequel, Secret Service in Darkest Africa, with Cameron's reprising the character of Rex Bennett, and the feminine lead taken by Joan Marsh playing Janet Blake, a British reporter.