As its title suggests, Big If is a precarious affair, as two siblings, a Secret Service agent and a computer programmer, try to keep their lives from falling apart. Following Bag Men, Mark Costello’s pseudonymous (he wrote it as " John Flood " ) 1997 novel of police corruption in mid-’60s Boston, Big If looks to widen its artistic scope. Bag Men was suspenseful, and its largely two-dimensional portrayal of urban vice and violence offered flashes of subtlety; Big If dips far deeper into the psyche, and it also rises to heights of mordant humor. In the end, though, the book’s characterizations overwhelm its structure and plot.

Jens and Vi Asplund grew up in Effing, on the New Hampshire coast, the children of a Republican insurance man who believed in everything but God. Jens wrote his first program, JENSISNUMBER1, at age 13; after getting a fellowship to Harvard, he abandoned his PhD. Now he’s married to the rich mortician’s daughter, Peta, they have a three-year-old son, and he writes " monster logic " at BigIf, a " massive multiplayer war game on the Web. Already he’s created Hamsterman, Seeing Eye, and Farty Pup (all self-descriptive monikers); up next is Monster Todd, a psychopathic grumpy teen of the murderous Columbine variety.

Gray-eyed blonde Vi is athletic but can’t make the starting basketball team at UNH, after which she joins the Secret Service, where she graduates seventh in a class of 27. It’s an election year, and she’s been assigned to guard the vice-president, who’s running for the top spot; the team includes lead agent Gretchen Williams, Tashmo from North Dakota and the Ronald Reagan glory days, and blonde bombshell Bobbie Taylor-Niles, " less a woman than an ocean liner of desire. " When she returns home the day before the New Hampshire primary, Vi finds Jens six weeks overdue on Monster Todd and looking at burnout while co-worker friends like Vaughn Naubek are getting fired.

Costello pores over his characters’ lives in sharp, sometimes poetic prose that recalls Rick Moody but also a hipper Joseph Heller. He’s at his best when he’s detailing, and occasionally lampooning, the complexities of the American working life. In his description of the world of the Secret Service, he balances the routine of the job’s comprehensive insulation of the VP with the agents’ obsessive mania and incestuous behavior.

The story of Vi’s mentor, Lloyd Felker, serves as a sad lesson about the failure of " the system " to protect its own from harm. A grand theoretician of the Dome — the atmosphere of safety created around public officials by their protection forces — Felker once devised innumerable assassination plots to see whether the Service could foil them, thus increasing the organization’s effectiveness. After his superiors grew uneasy about his knowledge and destroyed his research, he became an agent on the VP’s team. After going AWOL during a particularly chaotic stop on the campaign, he vanishes, later turning up dead. In a manner worthy of Kafka, Orwell, or DeLillo, the Secret Service man thus becomes a secret within his own milieu, then ceases to exist.

Costello has created a similarly entropic world within the offices of BigIf. One newlywed programmer couple spend their honeymoon at the office; another programmer dresses as a postal worker to " inhabit " more fully the character he is designing for the game. Although there’s something maudlin and unbelievable about the high jinks at BigIf, their juxtaposition with the paranoid world of the Secret Service fuels the book.

The ending, however, runs on empty. Granted, Jens’s Prospero-like tending of a fictional kingdom and Vi’s protection of an all-too-real nation play off each other smartly. The book’s climactic event, a surprising burst of violence, also connects the divergent lives of its central figures. But Costello spends too much time on each character’s interior drama. Jens keeps his job, Vi proves herself — and the book ends with a bit of a whimper. I expected a " then " as momentous as the title’s " if, " and it never comes.