Agent 13: The Midnight Avenger

Agent 13: The Midnight Avenger was the name of a novel series based on Top Secret/S.I. setting published by TSR, Inc. from 1986 to 1988. There were three stories in the series, following the actions of the protagonist referred to in the novels only as Agent 13, or simply, The Agent. It was written by Flint Dille and David Marconi.

There is also a source book based on the characters and settings in the series.(Agent 13 Novels)

The background of the series was set in the late 1930s, reminiscent of the popular pulps of the era. Graphic novel editions of the series were also published subsequently.

The primary antagonists of the series was a group known as The Brotherhood. They were a highly secretive organization formed by remnants of the legendary lost civilization of Lemuria. Lemuria had been an advanced civilization in the prehistoric age of mankind.

Lemuria was destroyed by ravaging horde of primitive barbarians. The survivors who escaped established a hidden base whereby they dedicated themselves to preserving their advanced knowledge, keeping their existence a secret from the world, but maintaining a network of agents working surreptitiously amongst the rulers.

Through actions of these agents, the Brotherhood kept an eye on the development of the world, intervening through indirect and subtle means to guide the course of history, and when they judged the time was ready, gradually release bits of knowledge, such as specific scientific breakthroughs, to the world.

In the story, the secret agents of the Brotherhood were responsible for preventing the sacking of Rome by Attila the Hun in AD 452, as well as being responsible for the advancements during the Renaissance.

It was not revealed, at first, when corruption set in, or whether it had been there from the beginning. Eventually, Itsu, known as the Hand Sinister, one of the paramount leaders of the Brotherhood, seized full control of the Brotherhood, and began using it as a tool to dominate the world. Its agents acted to infiltrate the major governments of the world and set the world on a path towards globally destructive war, which would give them the opportunity to become its master.

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Wikipedia