The PM’s head sank into his hands, and Dr Gall winced inwardly at the sight. After all the country had been through with Covid-19 – the lockdowns, the lay-offs, the closures, the devastation to the economy and all the mortality on the wards – this was hardly the news she wanted to deliver.

She saw the PM raise his head and come up shaking it in disbelief, his bleary blue eyes fixing the national security adviser with a beady glare. ‘No,’ he said. ‘It just doesn’t make sense. Why would they choose Norwegian territory for this when they’ve got God knows how many Arctic islands of their own to mess around on? If you’d told me this had happened on – what’s that place? – Novaya Zemlya, then I could believe it.’

‘It’s a mystery,’ conceded the national security adviser, clearing his throat, ‘but the evidence is still compelling. The question now is, how do we respond?’

‘Hold on a moment,’ said the PM. ‘First things first. Right now, today, at this moment, is there a risk of infection to the general population?’

Dr Gall took her time answering. She had not reached the peak of her profession by rushing to conclusions. ‘As of this moment, PM,’ she said carefully, ‘the outbreak is contained. The Arctic scientists who were exposed have been isolated and quarantined. But what’s worrying us, and this is why I’ve asked for this meeting at such short notice, is that we have to assume that someone, a malevolent actor, may possess this virus and the means to release it.’

Once again, the PM lowered his head, as if he were studying the patterns of the carpet intensely before responding. ‘You say this second virus was “deliberately inserted” into the first?’ he finally asked.

‘Yes,’ Dr Gall replied. ‘That is correct.’

‘But how can you – how can we – be so sure?’

Dr Gall was unfazed by his question. ‘If you’ll permit me, Prime Minister, I’d like to explain how my team came to this conclusion, and, believe me, it’s not one we reached lightly.’

He nodded for her to continue.

‘Working in our Bio-safety Level 4 laboratory at Porton Down, our scientists extracted the nucleic acids – that’s the DNA – from the live patient samples we were sent by the Royal Free. We applied that to an analyser in our Level 3 lab and simultaneously examined the results in the EM.’

‘The EM?’

‘Sorry, the electron microscope. The results were unequivocal. The genetic sequence we are looking at simply does not occur in nature. This is a synthetic virus, possibly – and I know I’m straying outside my tramlines here – but, yes, it’s perfectly plausible that it was created as a biological weapon.’

‘Right …’ The PM was still thinking hard. ‘So how do we nail this down? If we’re going to respond, we need to be one hundred per cent certain of who’s behind it.’