HETE was Dinesh’s dream project, which he’d been planning since his undergraduate days: Human Excrement Treatment Ecosystems. An ordinary composting toilet could deal with human waste in situ, but it was still far too expensive and finicky to be much help to most of the people who faced a chronic risk of disease from poor sanitation – let alone those caught in the aftermath of a flood or an earthquake. The aim of the HETE project was to develop a whole portfolio of microbial communities that could render human waste safe in almost any situation, with an absolute minimum of labour and no expensive infrastructure. Disease prevention was the first priority, but in most cases there would also be useful by-products, such as fertiliser, solid fuel or biogas. In the most ambitious versions Dinesh had sketched out, a single ecosystem would be capable of being pushed between three or four different equilibrium states simply by nudging the population ratios of the various microbes. That way, broken or partly flooded latrines in a disaster area could be reconfigured easily – perhaps even automatically – to focus on destroying pathogens as rapidly as possible, and then switched back into more productive modes when the emergency was over.

Shen and Judith excused themselves; they’d already overrun their lunch hour. Nasim asked Dinesh if he wanted to share her ragoût – it was more filling than she’d anticipated – but he was too excited to eat.

‘My great-grandfather spent his entire life mopping out communal latrines,’ he said, ‘from the age of ten until the day he died. And there are still people doing the same job today. Human beings sweeping shit into drains that take it straight into the rivers.’

‘I am trying to eat,’ Nasim reminded him.

‘Sorry. I know it’s not a pleasant subject. I just want my own grandkids to be able to say that nobody is stuck with the same disgusting work.’

‘Yeah. I hope so, too.’

‘This is going to be a huge challenge,’ Dinesh admitted soberly. ‘The microbes living in our gut already outnumber our own body cells ten to one. Now we have to mimic and extend and improve upon that system, outside the body, in a safe, robust way. Dozens of species, thousands of genes, millions of interactions.’ He looked up at Nasim and smiled. ‘We’ll need the best bioinformatics expert we can find.’

‘Aha.’ Nasim put down her fork. It seemed everyone was trying to ambush her today.

‘Of course I’d have to follow standard procedures,’ Dinesh explained, almost apologetically. ‘I’d have to advertise the job and look at all the applicants. But from your experience here alone, I’m sure you’d leave everyone else for dead.’

‘Umm…’

Dinesh laughed. ‘I promise you, you won’t need a face mask. You can sit in a nice clean office analysing metabolic networks all day; nobody’s going to ask you to dig pit latrines.’

‘Can I think about this?’ she pleaded. Turning down a bribe from that idiot Caplan had been easy, because she’d simply had no power to give him what he wanted. But not only was Dinesh’s project worthy, she couldn’t even claim that it was beyond her ability.

Dinesh seemed to sense that he was losing her. He said, ‘I know the brain will always be sexier than the bowel. I didn’t exactly run away from the chance to work with Redland myself. But if we’re going to use technology to improve ourselves, this is the place to start: engineering a second gut that sits in the ground, banishing cholera and turning waste into fuel and fertiliser. Isn’t that every bit as amazing as a brain implant, in its own way? You could even think of it as a rehearsal for the HCP – because some of the deep, underlying network dynamics is sure to be the same. It wouldn’t be taking you far from your current path. It would all be experience; nothing you learnt would be wasted.’

With that, he ran out of steam; he just stopped and waited for her reply. Nasim couldn’t argue with anything he’d said, and though she still felt somewhat flustered to be put on the spot, she could hardly blame him for asking. Every time he’d discussed the project with her in the past, she’d told him how much she admired the idea.

But she’d worked too hard to get where she was to risk taking a detour. It was one thing to say that, in principle, it was all good experience, but she knew what the competition would be like for the HCP, and she knew which projects would shift her résumé towards the top of the pile, and which would shift it towards the bottom.

She said, ‘You’ll find someone else for the job. Someone who’s as keen on the whole thing as you are.’

Dinesh slumped against the table theatrically, trying to look suitably disappointed, but he was obviously still elated that the project was going ahead at all. ‘Ah well. If you’d said yes that would have been perfect, but it was too much to expect.’

When he’d left, Nasim sat toying with the unappetising remains of her cold ragoût. How would it feel, she wondered, to know you’d been part of an endeavour that had saved a few million lives? Such a triumph was no foregone conclusion, of course, but now that she’d ruled out any part in it for herself it was hard not to feel a twinge of regret. Fate and distance had robbed her of her chance to rage against the ayatollahs; missing out on the war against cholera and dysentery had been her choice alone.

Still, the brain beckoned. Trying to turn a blurred jigsaw puzzle of snapshots from a thousand dead finches into something that could mimic their song was a very strange job, but she had to keep hoping that it would be good for something eventually.

Martin left his office at ten o’clock in order to cover the protest scheduled for noon outside the Majlis, but by the time he and Behrouz arrived at Baharestan Square the crowd already filled the street and they could get no closer than the Mosque of Sepahsalar, a hundred metres south of the centre of the gathering. Martin’s permit to travel to Shiraz had, unsurprisingly, come too late for him to cover the big march there the week before, but it looked as if the Tehranis were determined to outdo their cousins and reclaim the record for the biggest demonstration since the fall of the Shah. Police lined the street, and though they were heavily outnumbered and were not intervening so far, every one of the protesters would be aware of the bashings and shootings by militia in this very location, just three years before. Simply being here took a great deal of courage.

The Mosque of Sepahsalar also functioned as a madrassa, and Martin took the opportunity to buttonhole a few of the young men who were squeezing their way through the crowd to reach its gates. Most of these pious Islamic students turned out to be noncommittal, rather than angrily opposed to the protests. ‘The people have many legitimate grievances,’ one ventured. ‘I won’t march with them, but they deserve to be heard.’ The uprising had become far too broad to be dismissed as a conspiracy of traitors and stooges; apart from a solid core of die-hard loyalists who refused to accept any criticism of the regime, many conservative Iranians had started to take a highly jaundiced view of the status quo. Once your children had been jobless for a decade, the streets were flooded with heroin and the guardians of morality had proven themselves to be hypocrites, what was left to fear from reformists who preached transparency and offered new economic ideas?

Certainly the demographics were changing: this crowd was dotted with grey-haired men in suit coats, and there were quite a few middle-aged women. Most of the latter declined to be interviewed, but Martin managed to get a quote from one woman who looked to be in her fifties. ‘I marched against the Shah,’ Behrouz translated, ‘because he shot his own people and imprisoned his opponents. Why wouldn’t I march against thugs in clerical robes who think they can settle disputes the same way?’