‘“The Church needed reform but not schism, yet many in power could not see it that way. Among them was the Bishop of Siena, Ludovico. He had most to fear because he had turned his palace into a scandal of carnal pleasures and gluttony, corruption and vice. He sold indulgences and granted final absolution to the rich only in exchange for all their wealth. Yet here in his own city, almost beneath his walls, lived a young woman who by her example put him to shame and the people knew it. She did not preach, she did not incite, as Savonarola had done, but he began to fear her nonetheless.”’

From the judges’ stand in the Piazza del Campo the treasured Palio was ceremoniously handed down to the leaders of the winning Contrada and the banners bearing the device of the porcupine waved frantically in triumph as they prepared to chant their way to the Victory Banquet.

‘We’ve missed it all, honey,’ said the American wife as she tested her damaged ankle again and found it much better. ‘There’ll be nothing left to see.’

‘Just a tad longer. I promise we’ll see all the celebrations and the pageantry. It lasts till dawn. So what happened to her? What happened to Catherine of Mercy?’

‘“The bishop’s chance came the following year. It had been a summer of intense heat. The land parched, the streams ran dry, animal and human filth lay thick in the streets, the rats exploded in numbers. And then a plague came.

‘“It was another incidence of the dreaded Black Death, which we now know as bubonic or pneumonic plague. Thousands fell ill and died. Today we know that this disease was spread by the rats and the fleas that lived upon them. But then people thought it was the visitation upon the people of an angry God, and an angry God must be appeased with a sacrifice.

‘“By then, to distinguish herself and her three acolytes from other sisters in the city, Caterina had devised an insignia which all four wore on their habits: the cross of Jesus but with one broken arm to signify His grief for His people and the way they behaved to each other. We know about this because it was carefully described by the old father confessor who wrote down his memories years later.

‘“The bishop declared this design to be a heresy and fomented a mob, many of them paid with coin from his own coffers. The plague, he decreed, had come from that courtyard, spread by the mendicants who slept there but thronged the streets in the daytime. People wanted to believe that someone was to blame for their sickness. The mob descended on the courtyard.