The monk led them the length of the nave, the austere granite columns soaring to the high ceiling, belittling mankind’s stature before the Almighty, but offering sanctuary to the very poor who could not afford lodgings at any price. They huddled to sleep along the side walls and in the upper gallery, while others lined up to confess their sins. The dull chanting of Latin echoed through the vast space as pilgrims sought indulgences.

They heard John Jacob’s quick footfall behind them. ‘A wonderment, isn’t it?’ he said, impressed by the spectacle, his face flushed from catching them up.

‘Now that’s a wonderment,’ said Killbere as across the transept before them a silver censer, the size of a modest church bell, streamed forth incense. Eight robed men hauled a pulley and swung the heavy object back and forth at speed. Blackstone tapped the monk on the shoulder and pointed to the rapidly swinging censer, his look asking the question his lack of Spanish could not.

‘Botafumeiro,’ said the monk. Accustomed to those who travelled the French route into Spain, he went on in stumbling French: ‘Charcoal and incense. It masks the pilgrims’ stench and kills disease.’

‘If it ever comes off that pulley it’ll kill more than disease,’ said Killbere.

‘I told you there was no need to wash your shirt,’ said Blackstone as they turned along the right-hand side of the transept, where the monk gestured for them to wait. The three men watched in quiet fascination, well clear of the hurtling censer, as hundreds of pilgrims knelt in prayer, or pressed their backs against the wall as the thick incense cloaked the pillars.

‘Sir Thomas?’ Blackstone turned when beckoned. The monk gestured for him to enter the room off the transept. Blackstone signalled Killbere and John Jacob to stay where they were. As he stepped inside the room, he saw it was the antesacristía. There, a man who appeared to be of some importance stood waiting while an older man in more elaborate ecclesiastical robes was being helped to dress for mass. The latter Blackstone guessed was the Archbishop of Santiago de Compostela.

Blackstone waited at a respectful distance, ignored by the Archbishop.

‘I am Peralvarez, the dean here.’

‘And I beg an audience with the Archbishop. I have travelled a great distance on the orders of the English Prince of Wales and Aquitaine.’

‘Your name?’

‘Sir Thomas Blackstone.’

‘On request from the Prince?’ said Peralvarez as if confirming the truth. ‘His grace is soon to give the Most Holy Sacrifice of the mass. There is little time if you are here to seek indulgences or confession.’

The older man, who stood a few yards behind the dean, allowed his attendant to fuss over his vestments. ‘I am Suero Gómez, Archbishop. What is it that brings you here?’