Christopher Buckley’s “Boomsday” (Twelve, 318 pages, $24.99) is based on a wickedly funny idea. With an estimated 77 million baby boomers looking at retirement, the bottom could be falling out of the Social Security system in the not so distant future. One theoretical solution would be a mass suicide of old boomers, thereby relieving the tax burden on younger generations.

Such is the modest proposal of Cassandra Divine, and she’s not kidding. “A morally superior twenty-nine year old PR chick,” Cassandra has a vendetta against her father, a second-generation Irish American who squandered her college money on a business scheme. Daddy is, to put it simply, a real jerk — “He managed to make it sound as though selling his share in the [company] plane would be tantamount to economic suicide. The family would be out on the street, eating potatoes that fell off trucks. Irish ancestry is a reliable provider of poverty metaphors.”

In fact, no one in “Boomsday” is a beacon of moral integrity. Cassandra’s boss at the Public Relations firm, Terry Tucker, built his company “on the premise that those with a debatable claim to humanity will pay through the snout to appear even a little less deplorable.” How bad is Terry? Well, he had apprenticed under the legendary Nick Naylor, an ace lobbyist for the tobacco industry and the star of Mr. Buckley’s funniest and best novel, “Thank You for Smoking.” Cassandra’s next boss, Rep. Randolph K. Jepperson IV, a ruthlessly amoral limousine liberal, is no bargain either. He sponsors Cassandra’s “voluntary transition” — i.e., suicide — bill so long as it suits his political ambitions. He’s one of those politicians, Terry tells Cassandra, “born with Original Spin.”

Cassandra — her name is a giveaway that the author is using her to sound his own doomsday theory — becomes a hugely influential blogger, and she and Mr. Buckley have all their figures lined up. (“When the going gets tough,” Mr. Buckley writes, “the tough get blogging.”) When Social Security began, we are reminded, there were 15 workers to support each retiree. Now the ratio is about three-to-one, and it appears to be heading towards two-to-one. “You can run from that kind of math,” she says, “but you can’t hide. It means that someone my age will have to spend their entire life paying unfair taxes.”

Satire doesn’t have to be fair to be funny, but it does have to be plausible. Mr. Buckley has his agenda, and he presents it in an amusing and convincing fashion, all the more so since there are no arguments presented to the contrary. Since Social Security is the most boring subject in the world, we owe Mr. Buckley a debt for putting the subject in front of us in the form of a highly readable novel with flip-page howlers. But the idea that such a movement could be a hot button issue in a presidential race is so silly that the momentum of “Boomsday” begins to dissipate before the midway point. (One of the reasons Jonathan Swift’s scathing essay, “A Modest Proposal,” on solving the Irish population problem by having Englishmen eat Irish babies, outraged so many was because some people — at least some English landlords — were willing to consider it.)

What seems to fuel Cassandra’s rage is not the coming Social Security crisis at all but disgust at her father’s generation: “Our grandparents grew up in the Depression and fought in World War II. They were the so-called Greatest Generation. Our parents, the Baby Boomers, dodged the draft, snorted cocaine, made self-indulgence a virtue.” Yes, but weren’t they also the generation that helped usher in civil rights, fought the Vietnam War, and ultimately voted for President Reagan — twice? It doesn’t sound so much as if Cassandra is advocating suicide as the extermination of baby boomers on one side of the political spectrum.

But that’s not all that’s wrong with “Boomsday.” Mr. Buckley strains hard to find a sharper satirical point while avoiding much more obvious ones. Under President Peachum (a President Bush stand-in whose campaign motto is “He’s doing his best. Really.”), “The United States was currently engaged in six wars. The military was stretched to such a point that it was now safe for countries to invite the United States to attack them. The latest humiliation was Bolivia’s unilateral declaration of war.” This is not only funnier stuff than the mass suicide idea, it’s on a lot more people’s minds right now, probably because it seems much more likely to lead to boom and doom. But Mr. Buckley’s fictional president earns only a flesh wound from his rapier. Mr. Buckley is just six years younger than President Bush. It’s a shame he didn’t choose to pick on somebody closer to his own age.

Mr. Barra reviews books for Salon.com and was a finalist for the National Book Critics Circle Nona Balakian Citation for Excellence in Reviewing.