‘How kind,’ Sophy primly rejoined, ‘but, thank you, no. I’m not all that put out. It’s only—’

‘Well?’

‘I’ve got a theory about walls.’

‘Walls?

‘Surfaces. Any surfaces.’

‘Do explain yourself.’

‘You’ll be profoundly unimpressed.’

‘One never knows. Try me.’

‘Mightn’t surfaces—wood, stone, cloth, anything you like—have a kind of physical sensitivity we don’t know about? Something like the coating on photographic film? So that they retain impressions of happenings that have been exposed to them. And mightn’t some people have an element in their physical make-up—their chemical or electronic arrangements or whatever—that is responsive to this and aware of it?’

‘As if other people were colour-blind and only they saw red?’

‘That’s the idea.’

‘That would dispose rather neatly of ghosts, wouldn’t it?’

‘It wouldn’t be only the visual images the surfaces retained. It’d be emotions too.’

‘Do you find your idea an alarming one?’

‘Disturbing, rather.’

‘Well—yes.’

‘I wonder if it might fit in with your Simon.’

‘Ah,’ ejaculated Grant, ‘don’t remind me of that, for God’s sake!’

‘I’m sorry,’ Sophy said, taken aback by his violence.

He got up, walked away and with his back turned to her said rapidly, ‘All right, why don’t you say it! If I object so strongly to all this show-off, why the hell do I do it? That’s what you’re thinking, isn’t it? Come on. Isn’t it?

‘If I am it’s no business of mine. And anyway I did say it. Up above.’ She caught her breath. ‘It seems ages ago,’ said Sophy. ‘Ages.’

‘We’ve dropped through some twenty centuries, after all. And I’m sorry to have been so bloody rude.’

‘Think nothing of it,’ Sophy said. She looked up at the sharply lit head of Mithras. ‘He is not very formidable after all. Plump and placid, really, wouldn’t you say? Isn’t it odd, though, how those blank eyes seem to stare? You’d swear they had pupils. Do you suppose—

She cried out. The god had gone. Absolute darkness had closed down upon them like a velvet shutter.

‘It’s all right,’ Grant said. ‘Don’t worry. They do it as a warning for closing time. It’ll go on again in a second.’

‘Thank the Lord for that. It’s—it’s so completely black. One might be blind.’

‘“All dark and comfortless”?’

‘That’s from Lear, isn’t it? Not exactly a reassuring quotation, if I may say so.’

‘Where are you?’

‘Here.’

In a distant region there was a rumour of voices: distorted, flung about some remote passage. Grant’s hand closed on Sophy’s arm. The god came into being again, staring placidly at nothing.

‘There you are,’ Grant said. ‘Come on. We’ll climb back into contemporary Rome, shall we?’

‘Please.’

He moved his hand up her arm and they embarked on the return journey.