AT 4am one Sunday four weeks ago Andy Darley left his home in Feltham, Middlesex, and climbed into his car to drive the 114 miles north to Wakerley Great Wood in Northamp-tonshire — his third such trip in four days.

He was not the only one on the roads early that morning. Darley, a journalist turned web designer, reckons he was just one of 30-40 treasure hunters who were scouring parts of the royal forest of Rockingham.

The prize they were seeking was the Receda Cube, a sacred object “stolen” from the fictional world of Perplex City, an online puzzle-solving game that has fascinated and frustrated its tens of thousands of players for nearly two years.

As the final clues were cracked and the game reached its climax, it had become deadly serious: the prize for finding the cube was £100,000. Players who had previously worked together online to solve fiendishly complex brain-teasers were now keeping their own counsel, no longer willing to say where they were looking.

Darley, who once stood as a prospective MP for the Liberal Democrats, said he “felt a bit of a fool for abandoning real life” when he first drove to the forest. “I knew there was no chance of me finding anything, but I also knew I would regret it for ever if I didn’t at least try,” he said.

By Sunday, he knew he was in with a chance. And thanks to a combination of luck and the time he has spent on archeological digs, Darley was able to find the cube hidden six inches deep in the clay soil.

“You’re trying to convince yourself you’re wrong,” he said. “Until I could run my thumb against it and feel it was metal, I was still thinking ‘this is going to be a plastic bag that someone’s thrown away’. Then I knew I had found it and there was this surge of excitement.”

Yesterday evening, Darley was in London with other Perplex City players for a party thrown by Mind Candy, the Battersea-based company behind the game. A new season of shorter games will begin in April.

Michael Smith, Mind Candy’s founder and chief executive, said he was inspired by Masquerade, the book by Kit Williams which 25 years ago provoked a similar nationwide treasure hunt, and became a publishing sensation. With television presenter and author Bamber Gascoigne as his witness, Williams buried a golden hare in a casket near a monument in Ampthill Park, Bedfordshire. Clues to its location were hidden in the 16 paintings with which Williams illustrated Masquerade.

Smith said: “Perplex City is a complex 21st-century version of Masquerade. Our aim is to create an incredibly immersive entertainment experience.”

Complex is the key word here. Perplex City seeks to work on several different levels and to use a variety of media. On one level there is a science-fiction story — written by Naomi Alderman, who won the Orange award for new writers last year — about the theft of the Receda Cube from the Perplex City Academy, the efforts to recover it, and the murders that follow. The leading characters, such as the sisters Violet and Scarlett Kiteway, “write” web logs that players can read to find clues.

Mind Candy makes money (for now at least) by selling packs of collectible puzzle cards, often containing demanding mathematical challenges, the answers to which provide further pieces of the jigsaw.

The firm has sought to boost interest by creating offline events that bring players together. In one case, prompted by a press advert, between 30 and 40 players gathered on Clap-ham Common, London, where they were set a series of tasks. This culminated in a mole — supposedly an agent of the story’s villains, the Third Power — escaping in a helicopter.

Mind Candy has also created a magazine and produced an album of ambient electronic music by a Perplex City artist called Viard (actually the firm’s former art director). The album, The Silver City, includes a “secret” track with a disguised voice talking about events in Perplex City, revealing a little more information. Future games will make extensive use of online video.

“Consumers no longer want entertainment on one platform,” explained Smith. “They want to be surrounded by it. Rather than watching a film in a linear fashion, they are actually entwined in the story — it swirls around them.”

Smith argues that Perplex City has the chance to create a compelling new advertising medium. “There are huge changes going on within the world of advertising,” he said. The whole idea of interruptive marketing is becoming less effective. Consumers are spending less time engaging with television . . . and more time playing games and going online. Advertisers are looking at deeper ways of creating engagement with consumers.”

Smith said Mind Candy was talking with major brands about how they might feature in future seasons of puzzles. For example, he suggested, clues could be hidden in the inflight magazine of a sponsoring airline.

If you’re struggling to get your head round all this, you are not alone. Although some players throw themselves wholeheartedly into every aspect of Perplex City — Darley admitted there had been periods “when I’d be working pretty much full-time on it” — there are many more who have neither the time nor the inclination.

Mind Candy claims Perplex City has 50,000 registered players, but many of those have spent little time on it. Darley reckons the number of really active players capable of winning the prize was a few hundred in the first season.

Smith and his backers recognise this as a valid criticism, and future games will be shorter (from one to four weeks) and will offer more, smaller prizes. “It will become more episodic,” said Smith. “There aren’t that many people who have the time to spend hours every day looking at every web-site we launch and every clue we send out.”

Ben Holmes, of Index Ventures, which with Accel Partners invested $7m in Mind Candy in October, said the firm had done a good job of entertaining active players but needed to do more to attract more casual players.

“Michael and the team have been fantastically creative in their concept,” said Holmes. Perplex City’s ability to attract an active community, who spend hours online discussing how to solve puzzles, offered plenty of commercial opportunities, including merchandising, branding and advertising. “We are trying to create a product that reflects and builds on people’s changing desire in how to consume media,” said Holmes.

The ambition is to create a British firm to rival Second Life and World of Warcraft, the “virtual worlds” that have attracted millions of users and which fascinate many in the media and technology industries. World of Warcraft now has 8m users and is generating tens of millions of pounds for Vivendi Universal’s games division.

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