Blackstone watched two Moors standing at a double door of thick planks studded with ironwork and heavy hinges. ‘I think the King uses them as his personal bodyguard. This way.’ He turned into a doorway at yard level and immediately stepped into half-darkness. It was a storage area. The passage followed the length of the outer walls, broken by archways and bays built to accommodate materials. A waft of cold air brushed their faces.

‘Smell that?’ said Longdon. ‘Damp air. There must be a stairwell leading down.’ Blackstone’s centenar lifted the nearest oil lamp down from the wall and held it in front of him. He handed Blackstone a tarred reed torch, tipped the lantern and let the flame catch. Lantern and torch illuminated the way ahead. As they drew closer to the fresh air, the flames flickered. They saw a spiral staircase cut into the rock that would have passed unnoticed without light. Its narrow entrance was barely wide enough for a man’s shoulders. It was most likely used by child servants who could bend and twist their bodies up and down the steep spiral steps. Will Longdon tested the width. ‘I don’t think you’ll fit, Thomas. It’s too narrow. I would have to go down sideways.’

‘Use this,’ Blackstone said, offering the burning torch, exchanging it for the lamp. ‘Can you see anything?’

Longdon raised the lamp. ‘No.’

‘Let’s try it.’

Longdon followed Blackstone’s example and unbuckled his sword, which would have wedged against the walls if remained belted to his waist. It was a torturous descent, slowly moving sideways to accommodate the width of their shoulders, pressing the side of each foot into the risers. No light penetrated the funnel and the exertion soon had them sweating. They emerged into a small square room. The remains of dead birds littered the floor.

‘There has to be another way into here,’ said Longdon.

Blackstone barely fitted through the final turn. ‘Will,’ he called, extending Wolf Sword’s wrapped scabbard. The archer took it, allowing Blackstone to use both hands to pull and push himself free of the stair’s coils.

‘Here’s the passage, Thomas.’

Longdon bent low under an arch, torch extended, and then straightened to his full height. His voice echoed. ‘Big enough for you as well.’

Blackstone crept underneath and then stood upright. The limestone walls reflected more light and the hewn tunnel bore the scars of men’s efforts with pick and chisel. They felt the breath of cold air more keenly. Longdon led the way. Blackstone tried to gauge which direction the passage was taking them but after two hundred yards the floor dropped by several feet in a gentle slope and came to a dead end. Ahead was the rock face. They moved closer and then saw a gaping black pit to one side, unnoticeable at first because of a stone half-wall. They peered into the abyss.

‘It’s a well,’ said Blackstone.