‘Okay,’ he said. ‘Who would be following us?’

‘If I knew that, I wouldn’t need you to act as my tour guide.’

‘All right,’ Callum said, smiling at her. ‘You asked for it.’ He leant forward and spoke briefly to the taxi driver, who nodded. A few minutes later, they were deposited outside a tall Gothic tower. ‘The Powder Gate,’ Callum said. ‘Built by Vladislav the Second to add prestige to the adjacent Royal Court, which never really worked because the king fled riots in the Old Town centre a few years later and hid in the castle.’

‘I’m not a fan of Gothic architecture or royalty.’

‘Then you’re going to find Prague a great disappointment. It is one of the – maybe the – great Gothic masterpieces, though a lot of it is overlain and intermixed with the Baroque influences of the Counter-reformation.’

‘Explain.’ Out of the corner of her eye, Kate watched the Prius glide on past them, without slowing. Two young men in the front did not glance in their direction. Perhaps she was mistaken.

‘Well, I guess you’d say Prague’s golden era was when the Holy Roman Emperor Charles the Fourth chose to make the city the site of his imperial residence and determined to make it the most magnificent in Europe. I’ll show you the Charles Bridge in a minute. But after that, Prague became one of the hotbeds of the reform movement, led by Jan Hus – even you might have heard of him. He was burnt at the stake as heretics tended to be in those days. So when the Habsburgs take over, you get a strong counter-reformation led by the Jesuits, which is why you get all this incredible Baroque architecture overlying the Gothic, as if they were trying to obliterate all signs of what had gone before.’

‘Fascinating. Let’s get moving.’

They walked over the cobbles, weaving between thick crowds of tourists. ‘This is Celetná Street,’ he said, ‘which follows one of the oldest trading routes in eastern Bohemia. The name comes from the plaited bread rolls that were first baked here in the Middle Ages, but the reason so many tourists are here is because it was part of the Royal Route all the way from the Municipal House up to Prague Castle.’

It was a pretty street, sure enough, the houses with pastel façades and graffiti, inscribed for posterity in damp render, and uneven cobblestones that must once have rattled to the sound of horses’ hoofs, but now dealt with nothing more onerous than thousands of American trainers.

Callum took her away from Celetná Street to the Basilica of St James, which he informed her had been rebuilt in the Baroque style after a fire in 1689 allegedly started by agents of Louis XIV. ‘Don’t tell me you actually were a tour guide?’ she asked.

‘It was easy money as a student.’

‘How come you were a student here?’

‘We could choose to spend a second year abroad, so I came to Prague.’