The Rule of Four

The Rule of Four (2004) is a novel written collaboratively by American authors Ian Caldwell and Dustin Thomason. Caldwell, a Princeton University graduate, and Thomason, a Harvard College graduate, are childhood friends who wrote the book after their graduations. The Rule of Four reached the top of the New York Times Bestseller list, where it remained for more than six months.

Set on the Princeton campus, the story takes place over the Easter long weekend in 1999. The story involves four Princeton seniors, both friends and roommates, getting ready for graduation: Tom, Paul, Charlie, and Gil.

Tom, or Thomas Corelli Sullivan, narrates the novel, often finding himself distracted by his father’s death. His father was a professor who dedicated his life to studying the Hypnerotomachia Poliphili, a rare and mysterious book published in 1499 in Venice, Italy. The book, comprising complex allegory, is written in various languages. Throughout the novel, Tom struggles between being fascinated by the book and trying to pull away from the obsession that created a rift between his father and his mother and is now doing the same between him and his girlfriend, Katie Marchand.



Paul Harris is writing his senior thesis on the Hypnerotomachia Poliphili and has spent all four of his undergraduate years studying the book. He believes he is on the verge of solving the book's mystery.

Tom’s father was a close friend of Paul’s thesis advisors, Richard Curry and Vincent Taft. Taft developed a rivalry with both men in the quest to decode the Hypnerotomachia's 500-year-old secret. Tom's father found a letter referring to the book's supposed author, Francesco Colonna, and wrote a book called The Belladona Document, centering on the contents of the mysterious letter. However, it received a negative review from Taft, which led to the demise of the book’s popularity and Tom’s father’s academic career.

Paul discovers that the Hypnerotomachia contains a number of hidden and enciphered texts, with the solution to each one revealing a clue towards the next one. However, after solving a chain of several of these, he finds a text that says that there will be no more clues and he must solve the rest of the book on his own. He realizes that the entire book contains a message encoded by following a "rule of four," in which the message starts with one letter, then moves to a letter four rows down, then ten columns right, then two rows up, then six columns left, and repeating. Through days of tough work, Paul and Tom unravel a series of riddles, which they soon solved. The application of the "rule of four" method enables them to slowly piece together portions of a dark Renaissance secret.



The author of the book, Francesco Colonna, was a Renaissance humanist in Florence with a great passion for Greek and Roman literature. At the same time, a fanatical priest, Girolamo Savonarola, believed that Florence was gradually turning into a freethinking city, its people worshipping knowledge over God. As soon as he rose to power in Florence, Savonarola started the infamous Bonfire of the Vanities, a practice of burning books and art that seemed to contain elements of blasphemy. Colonna and confronted Girolamo Savonarola in an attempt to end the practice, but to no avail. Instead, Colonna started building a large underground vault to seal away a number of ancient books and pieces of art to preserve and protect them from the followers of the priest. On one occasion, to prove his stand, Francesco and two of his men walked into the raging inferno of the bonfire. As a result, Francesco met a fiery end. As Francesco had expected, his death sparked the cry against the reign of Savonarola, who was later hung and then burnt to ashes. Before dying, Colonna wrote the Hypnerotomachia, an encrypted book, in his effort to uplift humanism despite religious dogmas.

Paul's friend, Bill Stein, and his thesis advisor, Vincent Taft were conspiring together to steal Paul's thesis and claim credit for it, but were murdered by Paul's benefactor Richard Curry to prevent this from happening.

Tom, Gil, Paul, and Richard Curry are at Ivy Club, a Princeton eating club of which Gil is the president, when a fire breaks out. After much persuasion by both Tom and Paul to save each other from the fire, Tom jumps out of a window to be rescued by the firemen. Paul does not manage to do so, leading both Tom and Gil to assume that he must have died in the fire together with Curry.



Five years pass, and Tom is still traumatized by the event at Ivy Club. One day, he receives a tube in the mail containing an authentic ancient Botticelli canvas. The tube has a mysterious return address in Florence, Italy. Tom realizes the address is a code by his long-lost friend Paul Harris, urging him to head towards Italy soon.