Painting Mona Lisa. Jeanne Kalogridis

de’ Pazzi and Bernardo Baroncelli. He could not imagine why the visiting Cardinal should care so passionately about Giuliano’s presence at Mass; but if Lorenzo had asked him to come, then that was good enough reason to do so.

      He hoped, with sudden optimism, that Lorenzo might have changed his mind; that his anger had faded, and left him more receptive to discussion.

      Thus Giuliano rallied himself and, like a good brother, came as he was bidden.

       V

      Baroncelli hesitated at the door of the cathedral, as his objectivity briefly returned to him. Here was a chance to flee fate; a chance, before an alarm could be sounded, to run home to his estate, to mount his horse and head for any kingdom where neither the conspirators nor their victims had influence. The Pazzi were powerful and persistent, capable of mounting efforts to hunt him down – but they were neither as well-connected nor as dogged as the Medici.

      Still in the lead, Francesco turned and goaded Baroncelli on with a murderous glance. Giuliano, still distracted by his private sorrow, was heedless and, flanked by the uncertain Baroncelli, followed Francesco inside. Baroncelli felt he had just crossed the threshold from reason into madness.

      Inside, the air was filmed with smoke, redolent with frankincense and heavy with sweat. The sanctuary’s massive interior was dim, save for the area surrounding the altar, which was dazzling from the late morning light streaming in from the long arched windows of the cupola.

      Again taking the least-noticeable path along the north side, Francesco headed towards the altar, followed closely by Giuliano, then Baroncelli. Baroncelli could have closed his eyes and found his way by smell, measuring the stench of the poor and working class, the lavender scent of the merchants and the rose of the wealthy.

      Even before he caught sight of the priest, Baroncelli could hear him delivering his homily. The realization quickened Baroncelli’s pulse; they had arrived barely in time, for the Eucharist was soon to follow.

      After the interminable walk down the aisle, Baroncelli and his companions arrived at the front row of men. They murmured apologies as they sidled back to their original places. An instant of confusion came as Baroncelli tried to move past Giuliano, so that he could stand on his right, the position dictated by the plan. Giuliano, not understanding Baroncelli’s intent, pressed closer to Francesco – who then whispered something in the young man’s ear. Giuliano nodded, stepped backwards, and made an opening for Baroncelli; in so doing, he grazed the shoulder of the penitent, who stood waiting behind him.

      Both Francesco de’ Pazzi and Baroncelli watched, breathless, to see whether Giuliano would turn and make apology – and perhaps recognize the man. But Giuliano remained lost in his own misery.

      Baroncelli craned his neck to look farther down the row, to see if Lorenzo had noticed; fortunately, the elder Medici brother was busy bending an ear to a whispered comment from the manager of the family bank, Francesco Nori.

      Miraculously, all the elements were now in place. Baroncelli had nothing to do save wait – and pretend to listen to the sermon while keeping his hand from wandering to the hilt at his hip.

      The priest’s words seemed nonsensical; Baroncelli frowned, straining to understand them. Forgiveness, the prelate intoned. Charity. Love thine enemies; pray for those who persecute you.

      Baroncelli’s mind seized upon these phrases. Lorenzo de’ Medici had picked this Sunday’s priest himself. Did Lorenzo know of the plot? Were these seemingly innocuous words a warning not to proceed?

      Barconelli glanced over at Francesco de’ Pazzi. If Francesco had detected a secret message, he gave no sign of it; he stared straight ahead at the altar, his gaze unfocused, but his eyes bright with fear and hatred. A muscle in his narrow jaw twitched madly.

      The sermon ended.

      The elements of the Mass proceeded with almost comical swiftness: the Creed was sung. The priest chanted the Dominus vobiscum and Oremus. The Host was consecrated with the prayer Suscipe sancte Pater.

      Baroncelli drew in a breath and thought he would never be able to release it. The ceremony abruptly slowed; in his ears, he could feel the desperate thrum of his heart.

      The priest’s assistant approached the altar to fill the golden chalice with wine; a second assistant added a small amount of water from a crystal decanter

      At last, the priest took the chalice. Carefully, he lifted it heavenwards, proffering it to the large wooden carving of a dolorous, crucified Christ suspended above the altar.

      Baroncelli’s gaze followed the cup. A shaft of sunlight caught the gold and reflected blindingly off the metal.

      Again, the priest chanted, in a wavering tenor that sounded vaguely accusatory.

       Offerimus tibi Domine …

      Baroncelli turned to look at the younger Medici next to him. Giuliano’s expression was grave, his eyes closed. His right hand was clenched in a fist; his left hand clasped it, and both were pressed tightly to his lips. His head was bowed so he might have been praying. He looked like a man preparing to greet Death.

      This is foolish, Baroncelli thought. He had no personal enmity toward this man; indeed, he liked Giuliano, who had never asked to be born a Medici. His quarrel with him was purely political, and certainly not great enough to warrant what he was about to do.

      Francesco de’ Pazzi jabbed Baroncelli fiercely in the ribs, relating the unspoken message perfectly: The signal has been given! The signal has been given!

      Baroncelli released a reluctant, inaudible sigh and drew his great knife from its hilt. Hefting it overhead, he remembered all the dozens of phrases he had rehearsed for this instant; none of them came to his lips, and what he finally shouted sounded ridiculous to his own ears.

      ‘Here, traitor!’

      The church bells had just begun clanging when Giuliano looked up. At the sight of the knife, his eyes widened with mild surprise.

      Baroncelli did not hesitate. He brought the blade down.

       VI

      A moment earlier, Lorenzo de’ Medici had been engaged in courteous but muted conversation with Cardinal Raffaele Riario. Although the priest was finishing up his sermon, the wealthy power-brokers of Florence thought nothing of discussing matters of pleasure or business – sotto voce – during Mass. The social opportunity was simply too great to ignore, and the priests had long ago become inured to it.

      A scrawny lad, Riario looked younger than his seventeen years, and though he was currently a student of law at the University of Pisa, his enrolment there was clearly due more to his kinship with Pope Sixtus than any native intelligence.

      Nephew, Sixtus called him. It was the euphemism by which popes and cardinals sometimes referred to their bastard children. The Pope was an extremely intelligent man, but obviously had got this homely, witless boy on a woman with charms other than beauty or brains.

      Even so, Lorenzo was obliged to show the young cardinal a fine time while he was visiting Florence. Riario had specifically asked to meet with the Medici brothers and to be given a tour of their property and collection of art; Lorenzo could not refuse. This was the Pope’s so-called nephew – and though Lorenzo had endured public humiliation at Sixtus’ hands – even been forced to hold his tongue while the Medici were replaced by the Pazzi as the papal bankers – perhaps this was an overture. Perhaps Sixtus was trying to make amends, and this gangly young creature in scarlet robes was his emissary.

      Lorenzo was eager to return to the family palace to ascertain whether this was indeed the case; the cardinal’s visit would irritate him greatly if Sixtus was simply taking brazen advantage of Lorenzo’s generosity. It would be yet another insult.

      But