Some missions involve fetching items or fighting monsters; others include a variety of puzzles that are quasi-alternate reality games that require "searching the Internet" for clues with an in-game browser.

The game features an original present-day setting created by Funcom, which includes "magic, myths, conspiracies and dark horrors.

"[5] In the game, the player's character, living in the present day, joins one of three world-controlling secret societies attempting to repel, mitigate or exploit the attack of malign immortal beings in coastal Maine, rural Egypt, Transylvania, a quarantined section of Tokyo, a utopian community outside South Africa's Cape Town and (planned) a section of the river Congo; and to advance their society's agenda over that of the others.

Mission content bleeds into player faction headquarters in London, Seoul and the Dumbo neighborhood of Brooklyn, and into the game's transport network, along the subterranean branches of Yggdrasil in Agartha.

[2] The players will assume the roles of supernatural heroes who participate in a "future war between good and evil", fighting dark monsters that threaten the modern world.

H. P. Lovecraft's works, the Indiana Jones franchise and Stephen King's novels are major inspirations for the game's settings and storylines.

The character then travels to London, Brooklyn or Seoul to receive training and endure a variously-induced hypnotic flashback of the Tokyo disaster.

A black liquid called the "filth" bubbles up from beneath the mountain, rapidly corrupting the minds and bodies of all creatures who contact it and gradually revealed to consist of the dreams of old gods.

Also present on the island are the Order of Phoenician Sailors, a resentful global pirate/mercenary army, and the in-house soldiers and scientists of Orochi, the world's largest tech conglomerate.

The player is assisted by a mafia of black-marketeering mummies, by a millennia-old paramilitary resistance movement named the Marya, by a cagey eyewitness of old-testament events wielding what seems to be Aaron's Rod, and by Akhenaten's rebellious high priest and the seven of his own children he sacrificed in order to create seven avatars of the Egyptian pantheon, in the form of giant Sentinel statues.

The next location the character visits is Bacaş County, Transylvania, where an ancient human-fairy truce has been broken by an army of vampires besieging the local town.

The plot reveals this siege is at the request of their queen Mara, concealing her work to exploit another Filth source and gateway into other dimensions originally opened by the Orochi Group using Emma, a captive teenaged psychic.

The character later revisits the three main locations, and they slowly learn that all three major catastrophes are heavily linked to the Orochi Group and its mysterious leaders; Samuel Chandra and Lily Engel.

After announcing the development of The Secret World, Funcom project director Jørgen Tharaldsen informed the press that the game uses the same engine as Age of Conan.

[11] According to him, the game is story-driven and there is an overarching linear plot, as well as numerous side-quests, ranging from investigation to sabotage and hunting, since diversity of the gameplay will be another central point.

In an interview with GameSpot at the 2009 Penny Arcade Expo, Tørnquist and the lead designer Martin Bruusgaard revealed which playable factions ("secret societies") will be available in the game.

The factions are: the London-based Templars, pious zealots "who would burn an entire village down to get their hands on one demon"; the New York City-based Illuminati, Machiavellian pragmatists who "believe that it's a tough world where only the strongest will survive"; and the Seoul-based "Dragon", who take a neutral stance between the other two and are "all about deceiving, orchestrating chaos, and waiting patiently for its time".

[12] The same interview revealed that PvP areas of the game are located in the region called Agartha inside the hollow Earth, where the players will fight for the invaluable resource known as "anima".

[14] The pre-production of the game originally known as Cabal (and The Entire World Online in the earliest concepts) started in 2002,[8] but in mid-2003, most of the working team was transferred to the development of Dreamfall.

[8] The work on The Secret World was resumed in 2006, after Dreamfall shipped, with many of the latter's designers (including Ragnar Tørnquist) playing key roles in the former's development.

The company also revealed that over 750,000 gamers had applied to beta-test the game, significantly higher than for their previous MMO, Age of Conan: Hyborian Adventures.

[24] The first promotional material appeared on May 8, 2007, when a picture was leaked into the internet, containing a poem, a Knights Templar seal, and several sentences in Spanish, Norwegian, French, German and Hebrew.

Solving the puzzle gave the players 5 sets of coordinates, revealed several early screenshots from the game and marked the end of the first ARG.

[39] Funcom also had a panel advertising The Secret World at PAX East 2012 where people could play the game for the first time in preparation of the first beta test.

These beta weekends allowed players to explore the two area of the game, play the first two dungeons and experience the different introduction sequences for each of the three factions.

[1] The game was officially used in the film IRL and plays an important role in it, showing the main character's internal perception of the world and helps him find love.

Funcom claimed that mixed and poor reviews, coupled with the proximity of Diablo III, Guild Wars 2 and World of Warcraft: Mists of Pandaria launches, cut the sales of the game.

[57] In 2014, Human Equation acquired license rights for Funcom's Black Watchmen intellectual property (IP), which is a part of The Secret World universe.

The company intended to create a permanent alternate reality game with the Black Watchmen license as well as an accompanying comic book.

[3] Several new additions were added to the game post-launch, such as: the Dawn of the Morning Light storyline, the Agent System and the Occult Defense Scenario.