Put yourself in the shoes of a comic-book geek. You log on to a site that has been dropping clues about the genre's most anticipated film in years, engaging you in a labyrinthine search for its lead villain, only to discover that the latest stage in your quest is a trip to a secret location - which turns out to be a bakery.
On your arrival, you find a cake with a phone number scrawled in icing, which you call. Then, from inside the cake, a mobile phone chimes, followed by a message from the villain himself, recruiting you as one of his henchman.
Sounds like a comic buff's wet dream, yet, for some, this was far from the realms of fantasy. It formed one of the key stages in the elaborate viral marketing campaign that led up to the US release of the latest Batman film The Dark Knight, which has since grossed more than $300 million in US ticket sales in record time.
The campaign, which enticed its fans to an "alternate reality game", comprising everything from websites to nationwide scavenger hunts and faked murders, was the brainchild of the California-based agency 42 Entertainment.
The outfit, led by the president and chief executive, Susan Bonds, and Alex Lieu, its chief creative officer, has been behind many of the most popular ARGs of the past couple of years, including the Cannes Cyber Lion-winning Year Zero campaign for the rock band Nine Inch Nails, and the viral marketing for the movie Cloverfield.
However, the ARG for The Dark Knight has been its most popular so far, spanning 66 countries and achieving four times the audience of Year Zero, with peaktime hits on the associated websites in the tens of millions.
Discussing it for the first time ever, the agency (which doesn't like to publicise its campaigns in order to maintain their mystique) attributes its success to its collaborative relationship with the film-makers at Warner Bros, which enabled it to intertwine the online marketing with the film's storyline and the exceptionally crafted print campaign that backed it.
"The film-makers contacted us first and we read the script and discussed the themes and epic nature of the film, and settled on the multiple pieces of the equation that the film-makers wanted us to explore," Lieu explains. "These early discussions centred on creating a narrative that started at the end of the first film and met up with the beginning of the second, " Bonds adds.
To achieve this, the agency's 25-strong team of writers, designers, production teams and live events unit devised a 15 month-long game that galvanised the fanbase into a surreal global game of Cluedo, based around the director Christopher Nolan's vision of Gotham City, with Heath Ledger's Joker as the elusive murderous culprit.
Nick Emmell, Dare's planning director, says: "Traditionally, you can't find anything out about films until two weeks before release, but they were funnelling people into an immersive experience 18 months before the film came out."
It all began in May 2007, when campaign posters of Harvey Dent, Gotham's "white knight" politician, were plastered across cities in the US, accompanied by a campaign website. Things took a sinister turn, though, when The Joker's iconic red smile and black eyes appeared graffitied over the posters, driving people to a new website.
This tantalising interception by The Joker kick-started a race to reveal the first image of the villain.
The narrative of the game continued throughout the year with further campaign sites, mock political rallies for Dent and even a fake newspaper: The Gotham Times.
In July came another stunt at a San Diego comic conference, where defaced dollar bills bearing another URL were strewn around for players. They were then directed to gather outside, where a plane wrote out a phone number in the sky. Once they called the number, players were treated to a conversation between two of The Joker's henchmen and provided with a code that when entered on a website, began a scavenger hunt around the city for a trailer for the film.
This content became regarded as exceptionally valuable property, and by rewarding consumers who were demonstrating a passion for the film, the agency was creating both a sense of ownership among a core group, and setting those people up as ambassadors for the brand and the film's commercial partners.
Despite the views of some - Mark Cridge, the chief executive of glue London, says "the actual number of people who get involved throughout ARGs is minimal" - 42 Entertainment maintains that this "anti-broadcast" marketing model, built on a core group of players enjoying themselves, will lead to a broader dissemination of their experiences and build anticipation and excitement of the film's release among a wider audience.
As Lieu explains: "If you give the audience the chance to discover things for themselves, then the level of ownership is far greater and they become much more passionate advocates for the brand."