By Ian Caldwell and Dustin Thomason

Dial. 372 pp. $24

A riddling secret kept for 500 years in the encrypted pages of a "painfully, tediously difficult book," an enigmatic blueprint to hidden treasure, art-historical cover-ups of monumental Renaissance importance, evidence indicting Savonarola, passionate academic rivals with longtime grudges and deadly intentions -- sounds familiar, doesn't it? Add to that, in the short scope of 48 hours, two murders (maybe three), two conflagrations, at least three thefts, four hospitalizations, several assaults, an all-out brawl and buckets of blood, and you would expect The Rule of Four to be a pell-mell thriller seeking to capitalize on the tremendous popular success of The Da Vinci Code.

You would be about two-thirds wrong. Instead, in this first novel, long-time friends Ian Caldwell and Dustin Thomason have given us an unusual hybrid of adventure story and college novel; the tone and pacing are (most of the time) very different from that of a thriller. If they claim an influence, it is not Dan Brown but F. Scott Fitzgerald, who is invoked at the beginning of the book and cited throughout, not so surprising in a Princeton setting but sometimes a little at odds with the hugger-mugger. Other citations include Pynchon, DeLillo and Tom Stoppard, a tricksy bunch, and far from the land of suspense.

To the mix, they have added a recondite knowledge of cryptography, but also steganography, Rithmomachia, Horapollo's 15th-century book the Hieroglyphia and the kind of erudition required to solve such ancient conundrums as "What do a blind beetle, a night-owl and a twist-beaked eagle share?" This is the fourth of five cipher-riddles posed as clues to a pivotal Renaissance manuscript, and, no, the answer is not "wings." The truly intrepid reader can solve some code-breaking challenges along with the Princetonians. But only partly.

It is Easter weekend, April 2-4, 1999, and there has been an unseasonable snowstorm in New Jersey. Four seniors sit around their dorm room in Dod Hall, three of them, including the narrator, Tom, more or less at leisure, having turned in their senior theses on schedule, the fourth working against the clock to finish his -- though he has been researching it since his freshman year, and even earlier. Paul is a straight-A student, considered brilliant, and his unusual thesis, the fulcrum on which the plot turns, is an obsessive analysis of a "painfully, tediously difficult" volume published in 1499, the Hypnerotomachia Poliphili, which means "Poliphili's Struggle for Love in a Dream."

This is a real book illustrated by strange woodcuts, some of which are reproduced here; facsimiles of its pages can be found all over the Web. A Web site at MIT claims it was written by Leon Battista Alberti, though many scholars (and our authors) attribute it to Francesco Colonna, whoever he may have been. But the action takes place in 1999, and there is no English translation, which gives the authors (1998 graduates, Caldwell from Princeton, Thomason from Harvard) literary license to embroider. And they do. Indeed, I've never before seen so much elaborate embroidery in a book, except for the endless cross-stitching on the Bible's Revelation. But the elaboration is essential to the novel.

Scheduled for this evening at Princeton is a lecture by Paul's thesis adviser, Vincent Taft, and another mentor, Richard Curry, will also be on hand. Tom will attend the lecture too; both these men were one-time colleagues of his father, who dedicated much of his own life and academic career to the Hypnerotomachia (the reason Paul first sought Tom out as a friend). It is also Tom's girlfriend's birthday. And in honor of the snowfall, sophomores of both sexes will be running the Nude Olympics. First, though, the roommates take time out to play a risky and quite illicit chase game in the network of steam tunnels under the campus. These events entwine with one another, which makes for a lively beginning and sets the scene for the ensuing conflicts.

Just after the friends emerge from the tunnels, at the 11th hour, Paul gets a completely unexpected key to his research, a Renaissance diary, mentioning Colonna, which supposedly disappeared decades earlier. He can keep it for only a day and must not let it out of his hands. Within a couple of hours, one of Paul's mentors has loudly attacked the other in public, and the grad student who supplied the diary to Paul has been murdered. Paul seems to be increasingly involved in bizarre events, and Tom, forgetting all about his girlfriend's birthday, tries valiantly to disentangle his friend from a fast-spreading web of suspicion. Events happen rapidly and melodramatically, leading up to the Ivy Club costume ball on the following night, where chaos breaks out.

But here let's stop, as the novel often does, to consider events of the past, not only of five centuries ago, but also of Tom's childhood, of the relationships among the earlier generation of Hypnerotomachia scholars as well as among the four roommates during their four years of college friendship. To a degree, this is meant to be a novel of character, probing the strong theme of loyalty and betrayal. For students, these Princetonians are remarkably strait-laced: You won't find the drugs that mellow the pages of Michael Chabon's or Donna Tartt's college novels, the only heavy drinker we meet is despised by everyone else, the sex is mild and off-stage. The four won't even indulge the adolescent pastime of downloading songs from the Internet.

Just about their only weakness -- aside from a fondness for Audrey Hepburn movies, of all things -- is an inclination to lie to grown-ups. Unlike the treacherous older generation, they pride themselves on their allegiance -- which these tumultuous two days will test starkly. They are broadly drawn: charismatic Charlie, set for med school and occasionally stung by a hint of anti-black bias; Gil, president of Ivy and banker-to-be; brainy but erratic Paul. And then there is Tom.

As narrator, Tom presents himself much less clearly than his fellows. We see him through action, not introspection. But I wondered at several points if the authors actually knew what a wuss of a hero Tom is. He protests his love for Katie, "the girlfriend I didn't deserve to find," but does he know how much he doesn't deserve her? If there were a Seriously Bad Boyfriend Booby Prize, Tom would be a contender, and why Katie sticks around through months of neglect is almost more of a mystery than the Hypnerotomachia presents. Twice during Paul's years of labor, Tom has given, and then withdrawn, his support, despite Paul's near beseeching. Though he judges his classmates, Tom's position in the loyalty sweepstakes is uncertain. At the end of the book it seems that, yes, the authors do know, mostly anyway, and so does Tom -- who turns introspective at last. It's subtle -- Fitzgeraldean, actually -- and one of the reasons this odd book is interesting beyond its plot and puzzles.

Another reason is patches of excellent writing. Much of this is elegiac, as Tom muses over the past, but there's a long, lovely passage set in the present as Ivy prepares for the ball and the students begin to arrive. This promises well for the future of the authors, either together or separately. Next time, their ambition may vault lower and their presentation smoother, but meanwhile The Rule of Four is a great read on its own youthfully brash terms. The title, by the way, refers not (or not only) to the roommates or to their college years but again to the encryption in the Hypnerotomachia. It is never fully explained. *

Alice K. Turner, a former fiction editor of Playboy, is the author of "The History of Hell."