‘Hang on, hang on,’ said Luke, ‘I think you’ll find the Time Police have got this,’ and pulled out his scratchpad. Stabbing at it for a few seconds, he said, ‘We’re four hundred and seventeen yards from the Pontus Aemilius. We cross the bridge, travel two hundred and seventy-five yards south-west, turn left, then another one hundred and fifty yards north-west. We turn west, proceed for around thirty feet, climb six wooden steps on our left, pass through the broken door, along the passageway, out the window, through the garden and back to our pod located in the north-west corner opposite the well.’

There was a sudden silence.

‘Takes all the fun out of it, somehow,’ muttered Markham.

Whatever amateurish appearance they might present to the world, St Mary’s possessed a smooth escape procedure almost certainly born of long practice.

Peterson walked ahead in his purple-striped toga, jaw jutting regally and pushing his way through the crowds. People actually fell back and made way for him. He was followed by Luke, Van Owen and Jane, all keeping close together and their eyes modestly downwards. They were followed by Max, who appeared to be indulging in a sotto voce monologue concerning the overzealous nature of some security officers not a million miles away. Followed by Markham himself, carefully watching their backs and ignoring everything said to him.

Luke was not surprised to see that no one appeared to be taking any notice of them in any way. They crossed the Tiber safely and once on the other side of the bridge, he said cheerfully, ‘How far do you think we’ll get before . . . ?’ and as he spoke, from across the river and over the rooftops there came a great shout. One shout but many voices, reverberating from wall to wall, echoing across busy streets. Not of triumph or victory but a cry of despair – of grief – of a sudden and dreadful loss.

Around them, all street life stopped. People lifted their heads and looked fearfully at their neighbours. A gradual silence fell. Across from where they were standing, a small boy, crying for a treat denied, hiccuped into silence, his dark eyes big and frightened above tear-stained cheeks. Many stood like statues, frozen in mid-movement. As if the city had paused to draw breath before a mighty storm broke.

‘I don’t like the look of this,’ said Markham, quietly. ‘We might want to pick up the pace a little, guys.’