‘I’m so sorry.’ She ached to ask more but sensed he might tell her in his own time. They sat in silence, watching the clouds turn from orange to pink to mauve, then to purple and finally, fading into grey.

‘It makes you feel very small, doesn’t it?’ he said, at long last.

‘I hadn’t thought of it like that, but now you say it . . .’

‘We’re just insignificant little specks on a small rock in a universe of millions of other planets, all swirling around among an infinite number of universes.’

The idea made her brain ache. ‘I might be a speck, but I don’t actually feel insignificant. Not inside.’

His smile was like a gift, but it vanished almost as soon as it arrived. ‘You’re right, of course. But I do wonder why we’re all here, struggling away on this planet of ours. No one would miss us if we just disappeared.’

She paused a second, recalling Ma’s advice never to ask questions, but then dismissing it. ‘But you’re one of those important scientists developing clever secret things, aren’t you? That’s pretty significant.’

‘There you are wrong, I’m afraid. Yours is by far the most important work. The human race wouldn’t exist without food.’

‘Anyone can peel vegetables and cook pies, but what you’re doing is . . .’ she stopped herself. Of course she hadn’t a clue what he actually did.

‘We all make our contributions, and none is more or less important than another,’ he said, catching her gaze for a second. What an odd character, she thought; unlike anyone else she’d ever met, obviously brainy but so serious, with all this talk of universes and the rest. His face still reminded her of a shy, vulnerable animal, the eyes so dark that they seemed to be concealing something hidden and mysterious, but his expression was kind.

She remembered the pathos of the piece he’d played on the piano, and the question fell from her lips before she could stop it. ‘But why are you so fed up?’

‘A friend of mine died today.’

The shock of it caught the breath in her throat. ‘That’s terrible. I’m so sorry.’

‘And the worst of it all is . . .’

She hoped he wouldn’t start crying again; it made her feel so helpless. ‘You can tell me. It might help to share it.’

‘It’s probably my fault.’

‘How can it possibly be your fault? He was your friend.’

He shook his head. Of course he couldn’t explain. His work was top secret.

She sat down again on her ledge, feeling the rough stone beneath her fingers. It was odd, not like any rock she’d seen before; not striped or rough, but smoothed into rounded shapes. Now she looked more carefully, she could see that it was speckled with tiny stones and shells, like the sandcastles they used to decorate on the beach when they were children, and she remembered Poppa telling her about it.

The man was watching her. ‘It’s called Pulhamite,’ he said. ‘Cement mixed with sand and shells.’