But then, madness in great ones must not unwatched go. The two men led a slavish existence. Their only source of relief came in the form of weekly meetings on Saturday nights, when they would regroup at one or the other's apartment, or at an empty diner, and transform the one interest they had in common into a shared diversion: the Hypnerotomachia.

Winter had fallen that year when Richard Curry finally introduced Taft to the one friend of his who'd never fallen out of touch-the one Curry had met long ago in Professor McBee's class at Princeton, who harbored his own interest in the Hypnerotomachia.

Imagining my father in those days is difficult for me. The man I see is already married, marking the heights of his three children on the office wall, wondering when his only son will start to grow, fussing over old books in dead languages as the world pitches and turns around him. But that's the man we made him into, my mother and sisters and I, not the one Richard Curry knew. My father, Patrick Sullivan, had been Curry's best friend at Princeton. The two considered themselves the kings of campus, and I imagine they shared the kind of friendship that made it seem that way. My father played a season of junior varsity basketball, every minute of t on the bench, until Curry, as captain of the lightweight football team, recruited him onto the gridiron, where my father acquitted himself better than anyone expected. The two roomed together the following year, sharing almost every meal; as juniors, they even double-dated twin sisters from Vassar named Molly and Martha Roberts. The relationship, which my father once compared to a hallucination in a hall of mirrors, ended the following spring when the sisters wore identical dresses to a dance, and the two men, having drunk too much and having paid attention too little, made separate passes at the twin the other was dating.

I have to believe that my father and Vincent Tart appealed to different sides of Richard Curry's personality. The laid-back, catholic-minded mid-western boy and the fearsome, focused New Yorker were different animals, and they must've sensed it from the first handshake, when my father's palm vas swallowed in Taft's meaty butcher's grip.

Of the three of them, it was Taft who had the darkest mind. The parts of the Hypnerotomachia that fascinated him were the bloodiest and most arcane. He devised systems of interpretation to understand the meaning of sacrifices in the story-the way animals' necks were cut, the way characters lied-to impose meaning onto the violence. He labored over the dimensions of buildings mentioned in the story, manipulating them to find numerological patterns, cross-checking them with astrological tables and calendars from Colonna's time, hoping to find matches. From where he stood, the best approach was to confront the book head-on, match wits with its author, and defeat him. According to my father, Taft had always believed that he would one day outsmart Francesco Colonna. That day, as far as we knew, had never come.

My father's approach could not have been more different. What fascinated him most about the Hypnerotomachia was its candid sexual dimension. In the more prudish centuries after its publication, pictures from the book were censored, blacked out, or torn up entirely, the same way many Renaissance nudes were repainted with fig leaves when tastes changed and sensibilities were offended. In the case of Michelangelo, it seems fair to cry foul. But even today, some of the prints from the Hypnerotomachia seem a little shocking.

Parades of naked men and women are only the beginning. Poliphilo follows a gaggle of nymphs to a springtime party-and there, hovering in the middle of the festivities, is the enormous penis of the god Priapus, the focal point of the entire picture. Earlier, the mythological queen Leda is caught in the heat of passion with Zeus, who is shown lodged between her thighs in the shape of a swan. The text is even more explicit, describing encounters too bizarre for the woodcuts. When Poliphilo is overcome with physical attraction to the architecture he sees, he admits to having sex with buildings. At least once, he claims the pleasure was mutual.

All of it fascinated my father, whose view of the book understandably shared little with Taft's. Instead of considering it a rigid, mathematical treatise, my father viewed the Hypnerotomachia as a tribute to the love of a man for a woman. It was the only work of art he knew that mimicked the beautiful chaos of that emotion. The dreaminess of the story, the unrelenting confusion of its characters, and the desperate wandering of a man in search of love all resonated with him.

As a result, my father-and, at the beginning of his research, Paul-felt that Taft's approach was misguided. The day you figure out love, my father told me once, you’ll understand what Colonna meant. If there was truly anything to be known about it, my father believed it must be found outside the book: in diaries, letters, family documents. He never told me as much, but I think he always suspected that there was a great secret locked inside the pages. Against Taft's formulations, though, my father felt it was a secret about love: an affair between Colonna and a woman below his station; a political powder keg; an illegitimate heir; a romance of the kind teenagers imagine before the ugly bride of adulthood comes and snuffs out childish things.

However much his approach differed from Taft's, though, when my father arrived in Manhattan for a research year away from the University of Chicago, he sensed that the two men were making great strides. Curry insisted that his old friend join them in their work, and my father agreed. Like three animals in a single cage, the men struggled to accommodate one another, circling in suspicion until new lines were drawn and new balances struck. Nevertheless, time was their ally in those days, and all three shared faith in the Hypnerotomachia. Like a cosmic ombudsman, old Francesco Colonna watched over and guided them, whitewashing dissent with layers of hope. And for a while, at least, the veneer of unity endured.

For more than ten months, Curry, Taft, and my father worked together. Only then did Curry make the discovery that would prove fatal for their partnership. By then he had gravitated out of the galleries and into the auction houses, where the larger stakes of the art world lay; and it was as he prepared his first estate sale that he came across a ragged notebook that had once belonged to a collector of antiquities, recently deceased.

The notebook belonged to the Genoese portmaster, an old man with a crabbed hand who made a habit of remarking on the state of the weather and his failing health, but who also kept a daily record of all goings-on at the docks in the spring and summer of 1497, including the peculiar events surrounding the arrival of a man named Francesco Colonna.

The portmaster-whom Curry called Genovese, for he never gave his name-gathered the rumors about Colonna circling through the wharf. He made a point of overhearing the conversations Colonna had with his local men, and learned that the wealthy Roman had come to Genoa to oversee the arrival of an important ship, whose cargo only Colonna knew. Genovese began bringing news of incoming ships to Colonna's day lodgings, where he once caught Colonna scribbling notes, which the Roman hid as soon as Genovese entered.

Had it been left at that, the portmaster's diary would've shed little light on the Hypnerotomachia. But the portmaster was a curious man, and as he grew impatient waiting for Colonna's ship to arrive, he sensed that the only way to discover the nobleman's intentions was to see Francesco's shipping documents listing the contents of the cargo. Finally he went to ask his brother-in-law, Antonio, a merchant who sometimes trafficked in pirated goods, if a thief might be hired to enter Colonna's lodgings and copy whatever could be found there. Antonio, in exchange for Genovese's help in another shipping scheme, agreed to help.