From the introduction:
Everything is true. Every myth, every conspiracy, every urban legend. They form a secret world hidden in plain sight, a world of unspeakable terrors ruled by shadowy Secret Societies. Some months ago, an artifact was activated in the Tokyo subway system, unleashing the scourge of the Filth and triggering occult disasters world-wide. Now immortal champions rise to forestall the dawning of an endless night.
The following document is meant to provide a basic framework for adapting the setting of The Secret World to fifth edition Dungeons and Dragons, allowing players to take on the role of Gaia's chosen and do battle against the influence of the Dreaming Ones. Old mechanics have been altered, and new ones added to fit the lore of The Secret World and help translate its trademark ambiance. This is by no means a complete conversion, and as an amateur work it is not rigorously balanced, but it should provide a jumping off point for those interested in enjoying The Secret World in a tabletop setting.
Dark Days are here, sweetlings.