By all accounts, Daria Shipilova, 28, was a high-flying young scientist, respected by her managers and peers.

She had graduated from her medical university in Irkutsk, Russia, two years ago with a Red Diploma, the equivalent of a first-class degree.

Daria was headhunted for a career at the Irkutsk Anti-Plague Institute in Siberia, and had started publishing research papers involving study of the bacterium behind the notorious Black Death that so decimated the medieval world.

In her personal life, she was in love and appeared to have her whole life in front of her. Yet on Friday, September 25, she visited her institute for the final time.

The story is that she dropped a test tube containing the pneumonic plague pathogen at the laboratory. And that was how she succumbed to the disease.

The following Tuesday, Daria was rushed to Shelekhov District Hospital, where it appears she was initially treated for misdiagnosed acute coronavirus. 'Her relatives say the doctors treated her symptoms as a severe form of Covid right up until the end, put her on a ventilator, and antibiotics were administered too late,' said Miroslava, her former colleague.

On the eve of her death on October 2, panic gripped the scientific and medical fraternity, first in Siberia and then in Moscow. In the hours before she died, there were sudden moves to lock down her hospital and the Irkutsk Institute.

Miroslava revealed: 'From October 2, the entire inpatient section of Shelekhov hospital was closed for quarantine, with all 114 patients locked inside.'

Russia's chief sanitary doctor Anna Popova, 65, boarded a plane for a five-hour flight east to Irkutsk to take personal charge. Ironically, at her last Kremlin meeting with Putin on September 15, Popova had told him how Russian medics were vaccinating Mongolians against the plague.

She informed the dictator: 'A great deal of work is being done on the plague, it is an important infection which, unfortunately, continues to affect the world and probably always will.'

And this is what makes the story so odd. As Popova suggested, though serious, the plague in that part of the world is not unknown. In July, Mongolia's National Centre for Zoonotic Diseases (NCZD) confirmed a human plague case in Khovd province in the western part of the country. The centre warned that 17 out of 21 provinces were classified as plague-risk areas. Several cases have been reported in recent years, including fatal infections.

And yet there has been nothing like the kind of reaction we have seen in relation to Daria's death.

Why was she not treated with antibiotics which, as anyone working on human plague pathogens would know can be successful? Indeed, why did Putin's medical chief, feel the need to rush to Siberia where plague cases have cropped up from time to time for years?

Popova worked 'virtually around the clock' after Daria's death, according to regional governor Igor Kobzev. Yet, for unexplained reasons, she failed to utter a single word about the emergency even as her health watchdog, Rospotrebnadzor, sought to claim there is no crisis and tragic Daria died of a 'pneumonia of unknown aetiology'. The test-tube story was denied by Rospotrebnadzor which insisted that her infection and death were unrelated to her laboratory work.

It gets more curious. Pregnant women in the city of Irkutsk have been asked to fill out a 'plague' checklist. This was reported by blogger Ulyana Gavryunina. On October 5, she went for a check-up at the Irkutsk City Perinatal Centre. Her mother, who was accompanying her, was not allowed into the maternity ward. The centre introduced a restricted access regime on Friday, allowing only pregnant patients to enter.

'They explained to me that there was unconfirmed information about a virus that could be even more dangerous than the coronavirus, that it was unclear what kind of virus it was and how to deal with it. So, they introduced a quarantine, and it's unclear how long it will last,' Ulyana said.

Up to five local hospitals are now in lockdown – despite official denials. A patient at City Clinical Hospital No 1 insisted: 'We are under full quarantine. None of our relatives are being allowed in. We are not being allowed out.'

In quarantine, too, and unable to hold a funeral for their beloved daughter, are Daria's parents Nikolay and Svetlana, and her four siblings.

It is clear the real story is not being told. And, increasingly, there is speculation that Daria and the institute may have been involved in a research project on biological warfare or some genetically manipulated organism that mistakenly got out into the world.

Daria's funeral might, in time, tell its own story: will her coffin be zinc-lined and hermetically sealed, and against Russian tradition, unopened for the ceremony? This would indicate a serious infectious disease.

Locals have an eye for official obfuscation even if there are no confirmed additional cases of infection. 'They take us for idiots,' said one. 'Something sinister has happened in this institute which they cannot admit to,' said a medic in Irkutsk.

One commenter, Elena, remarked astutely: 'The more they reassure us, the more frightening it gets.'

Another, Svetlana, posted: 'They're already lying just for the sake of lying, automatically.'

So was it a mysterious strain of pneumonia? Or perhaps some other sinister unknown disease – an unusually powerful plague strain, for example – that was under investigation at Daria's laboratory for reasons suiting the Russian state?

We cannot be sure. But Cold War researchers say the institute where Daria worked maintained millions of doses of plague vaccine for use in wartime and trained specialists from military institutes. A former director, microbiologist Igor Domaradsky, later became a senior figure in the USSR's secret biological-weapons establishment.

There is no doubt about Russia's research into bio-warfare.

In August reports emerged of a mysterious facility on Lisiy (Fox) Island in Russia's Tver region. It lies in the Vyshny Volochyok reservoir, 170 miles north-west of Moscow.

Ukraine's GUR military intelligence warned that an accidental release of pathogens or hazardous chemicals from this facility could have serious consequences for people, livestock, and the surrounding environment.

Soldiers guarding the installation 'express fear in private conversations of contracting an unknown 'infection',' the GUR report claimed.

The complex, officially called the Centre for Experimental Physiology, was established on Putin's direct orders as a project of particular importance to Russia's 'defence capability and security'.

Military research into potentially lethal pathogens at Daria's institute would explain the panic following her death. And not just in Russia.

Ex-Soviet state Kyrgyzstan has ordered heightened sanitary controls at all its border checkpoints.

People, vehicles and cargo crossing its frontier were subjected to increased 'epidemiological surveillance'.

Uzbekistan, meanwhile, was 'taking measures to prevent the importation and spread of highly dangerous infections'.

Kazakhstan's Health Ministry took 'preventive measures' after monitoring the Irkutsk incident. With a mammoth 4,750-mile frontier with Russia, it was carrying out sanitary-quarantine controls at state-border crossing points.

In the US, a White House spokesman said: 'The Trump administration is aware of the outbreak, is monitoring it, and is evaluating possible courses of action.'

There are other oddities about the official response to the crisis.

Governor Alexey Tsydenov, from the neighbouring Russian republic of Buryatia, initially referred to Shipilova as 'the woman who died from plague'. Later, seemingly under Kremlin pressure, he stepped back to say 'may have died from plague'.

The authorities in nearby Baikalsk briefly cautioned residents not to travel to Shelekhov because of unofficial information about a plague case – and then they deleted the claim.

The director of the giant Irkutsk Aluminium Plant in Shelekhov imposed a mask regime on workers as a 'precaution'.

Meanwhile, friends of Daria are anxious to dispute key claims in this story.

Her university classmates are 'outraged by claims circulating that she may have violated procedures for working with a dangerous pathogen and then concealed what had happened,' reported Radio Svoboda.

'We are all in shock, especially over the accusations that Daria broke a test tube and kept quiet,' said friend Valentina. 'You don't understand – working at the anti-plague institute is quite prestigious and very interesting for graduates of our Medical Biochemistry faculty.

'Daria graduated in 2022 after six years of study at Irkutsk State Medical University.

'She was intelligent [and] responsible. The institute is excellent and they follow the rules strictly.'

But suppose Daria had become infected with some version of the plague. She would have known pneumonic plague 'is quite treatable if treatment starts very early,' said one colleague.

'It would not have been in her interests to hide it.'

What work Daria was undertaking in the days before her death remains a matter of conjecture. REN TV – owned by a media giant headed by Putin's lover Alina Kabaeva, 43 – reported that 'she studied the plague bacterium from natural plague foci [where bacteria live] in Siberia, Mongolia and the Altai and examined the body's immune response to infection. 'One scientific paper involving the researcher described experiments on white mice, including the study of the body's response after infection with pathogenic strains of plague.'

But the situation became murkier yesterday when it was reported by Russian medical publication Medvestnik that 'a criminal case was opened under the article concerning violation of sanitary and epidemiological rules which, through negligence, resulted in the death of a person.'

This clearly contradicts the official version from the health watchdog Rospotrebnadzor that her infection was unrelated to her professional duties and there was no laboratory accident.

When the story first broke, Russian-born, US-based epidemiologist Mikhail Favorov, 74, a veteran former US Centres for Disease Control official who previously headed its operations across Central Asia, and has investigated outbreaks of plague and other dangerous pathogens, warned that there was 'a lot of nonsense circulating' about the case. He said that the test tube story was 'laughable' while highlighting that Anna Popova's rush to Irkutsk showed a 'terrible, critical situation'.

He highlighted mistakes in Daria's treatment saying: 'I rather doubt she was treated with antibiotics.' If prescribed early these could have saved her.

Instead, the treatment she received could have put others at risk.

'It seems to me they diagnosed her with Covid because she was having trouble breathing and put her on a ventilator. It's absolutely hair-raising.'

He suggested a major cover-up was under way, but predicted the Putin system would not reveal the truth.

'We will not be told what really happened,' he stated.

He responded: 'I might be old, but I am not a fool.'