Still nothing happened. Eleven o'clock struck. Noon. With each passing minute, Nayler's hopes revived. Rumours of the reasons for the delay swirled across the crowd: that the House of Commons was at that moment sitting in debate and cancelling the verdict, that the King had agreed to abdicate in favour of his son, that the Dutch had offered half a million pounds to purchase a reprieve. He tried not to imagine what must be going through His Majesty's mind as he sat in the Banqueting House. Evil enough to cut off a man's head; cruel beyond measure to drag out his agony.

One o'clock came and went, and then, just before two, there was activity. The window opened, and through it poured a file of soldiers with their officers, followed by the executioner and his assistant, clad in long black woollen coats and black leggings, their faces covered by black masks, with grotesque ill-fitting grey wigs and false beards. The shorter of them carried an axe, its long shaft resting on his broad shoulder. A bishop appeared behind him with a prayer book open.

The King stepped out of the window last – a slight figure, bareheaded, scarcely five feet three inches, although he carried himself, as he always did, even in these final minutes, as if he were a giant. He went straight to the low block, and it was clear he was remonstrating with the officers at this affront to his dignity, that he should have to lie on his stomach to be killed. They looked at one another, shook their heads. The King turned his back on them. Producing a small piece of paper from beneath his cloak, he stepped to the front of the scaffold. He surveyed the soldiers, the cavalry, and the crowd beyond. He seemed to realise his words wouldn't carry, so returned to the middle of the platform and read his speech to the officers. Nayler could not hear a word of it, although by the following day it was printed and available to buy on half the streets in London. If I would have given way to an arbitrary way, for to have all laws changed according to the power of the sword, I needed not to have come here; and therefore I tell you (and I pray God it be not laid to your charge) that I am the Martyr of the people ...

The King unfastened his cloak and removed it, took off his jacket and handed it to the bishop, along with some glittering decoration. He stood in his white shirt in the freezing cold and gathered up his long hair into a cap. He did not tremble. He said something to the executioner and gestured again to the block in protest, then shrugged, got down to his knees and lay full-length, adjusting his neck on the block until it was comfortable. He stretched his arms out behind him. The executioner braced his legs apart and lifted the axe as far as he could swing it behind his shoulder. A few moments passed, then the King made a gesture with his hands, a graceful flick, as if he were about to launch himself into a dive, and the blade descended with such force that in the silence the sound of the blow could be heard all the way down Whitehall.

Blood jetted out of the severed torso. The nearest soldiers twisted aside to avoid the flow until it settled into a steady glug, like an upended barrel. The executioner, still holding the axe, picked up the head by the hair, strode to the front and showed the King's face to the crowd. He shouted something, but his words were lost in the great roar that rose from the spectators, a mingling of exultation, horror and dismay. Part of the crowd pushed forward through the distracted pikemen, who had turned to watch the spectacle, and darted between the cavalry. Nayler jumped down from the wall and loped across Whitehall after them.

Beneath the platform, the blood was seeping between the planks. It pattered in the kind of heavy droplets that herald the beginning of a storm. People were slipping and scrambling all around him. He held up his handkerchief and watched it spot crimson – once, twice, three times, the spots spreading across the linen fibres and merging to form a single patch – then he fought his way out into the winter afternoon, up Whitehall and back along the Strand to the chapel of Essex House, where his patron, the Marquess of Hertford, and his family were kneeling at the altar, waiting to hear the news.

Excerpted from Act of Oblivion by Robert Harris. Copyright © 2022 by Robert Harris. Excerpted by permission of Harper. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.