In the opening scenes of Walter Jon Williams' new novel, This Is Not A Game, the main character, Dagmar, descends from fantasy into grim reality. Dagmar is the chief designer of Alternative Reality Games for a company called AvNSoft. The games she creates have both an online presence, drawing in thousands of players—sometimes hundreds of thousands—and a real world aspect, with actual locations for actual events that are tied to and directed from the online scenarios. Sometimes, the games are purely for AvNSoft, but they also do custom games for clients.

Dagmar is returning from Bangalore after the completion of such a game, called The Curse of the Golden Nagi, built and conducted to promote a new mobile communications platform. The job had its frustrations—one being that Dagmar became involved with one of the principle actors, who turned out to be married—but the end result had been a success. She is looking forward to a stopover in Bali for some major relaxation.

Unfortunately, she must make a connecting flight in Jakarta, and as she lands the country is entering a phase of economic crisis and possible revolution. All connecting flights have been canceled, and she finds herself stranded in a five-star hotel that, as the local crisis develops, becomes an oasis for the transnationals caught within it. Step by stage by day, Jakarta is sunk into chaos, and Dagmar becomes acutely aware of the danger in which she's caught. But she has her phone, a powerful device, and she contacts her boss, Charlie, who quickly begins making arrangements to get her out, using any means he can find.

In this instance, that means hiring a team of mercenaries who will stage a rescue from the rooftop of the hotel—if they can get their hands on a decent helicopter within range and get through the troubled airspace around the city. Dagmar, in her hotel room, begins a series of more-and-more frustrating email exchanges with the leader of these mercenaries. Time progresses, the situation worsens, and it seems the mercenaries possess all the skills of the Keystone Kops. It would be funny if her life were not at risk.

Then she hits on the idea of using the online community of devoted gamers she has built up over the years. She sends word to the user group, and almost at once a congeries of bright, disparate people begins working on the problem. They are all over the world, employed in different professions, and in most instances they only know each other through the games they play online. Some of them never quite grasp that Dagmar's plight is real. The abbreviation TINAG is used over and over again—This Is Not A Game—to impress on everyone the seriousness of the situation, but a few never believe it. As one of them says when told again this really isn't a game, "Maybe yes, maybe no. But what difference does it make?"

As it turns out, none at all. The gamers trump the mercenaries and, through an improbable but effective series of arrangements, manage to get Dagmar safely out of the country. The community Williams depicts here turns out to be the ultimate Baker Street Irregulars, and the comparison is apt. Early on, a comparison is made between one of Dagmar's games and The Sign of Four, which proves to be not only apt but prophetic.

Upon Dagmar's return to L.A. and her job, the danger she thought she escaped follows her home in the form of a monstrous global plot involving international currency manipulation, centering on AvNSoft and eventually on her boss, Charlie. When one of the partners, Austin, is shot dead on the parking lot of the AvNSoft building—a murder Dagmar witnesses—she begins digging into the company history. Back when there had been three original partners, one of them had been ousted by the other two. The circle of friends from college—Charlie, Austin, Dagmar, and B.J.—are all part of a game they did not even know they were playing.

When Williams is good, he is very good—and this is one of his best. He dances across the lines that blur real world and gameplaying with elegance and an acerbic sense of consequences that denies the artificial separation between the two worlds. When games grow large and complex enough, he suggests, they become the real world. The more factors added in to "flesh it out," the more a game takes on all the unanticipated aspects of real life. In this case, greed, jealousy, murder—and, as an added wrinkle, international politics.

People get drawn in from the various and unexpected touch points of the game world and get mangled in the course of discovering they have crossed a line somewhere and now, This Is Not A Game. In many ways, it never was, as Dagmar learns.

On another level, Williams is exploring the parameters of so-called social networking in a sphere of global communication that separates people by nanoseconds through myriad links that often bypass the comfortable and comprehensible channels through which we expect events to transpire. The connections made with communities that have utterly divergent, yet occasionally sympathetic, interests demonstrate the potential for cause and consequence unmediated by "authorized" intercessors.

This Is Not A Game is a satisfying, well-written mystery offering much more than the gratifications of finding out Who Done It or even Why It Was Done. Williams is exploring the byways, inroads, and unmarked paths of an only partially-glimpsed new territory with enormous untapped potential. But he is also giving a primer in basic reality: nothing humans do as a community can be separated from the Real World. Just talking to someone has consequences.