Hospital staff who saved the lives of poisoned Russians Sergei and Yulia Skripal have revealed they did not expect the victims of the nerve agent attack to survive.
The Skripals had been found slumped on a bench on 4 March - but staff treating them at Salisbury District Hospital did not initially know the reason why.
Nursing director Lorna Wilkinson said a key moment came when policeman Nick Bailey was admitted with similar symptoms. "There was a real concern as to how big this could get," she said.
She told BBC Two's Newsnight: "Have we just gone from having two index patients having something that actually could become all-consuming and involve many casualties? Because we really didn't know at that point."
And ward sister Sarah Clark, who was on duty that night, added that there were fears that the hospital's staff might end up being affected.
She pointed out that they had not, at that stage, "taken any extra precautions in terms of protecting ourselves".
When the nature of what they were facing became clear, hospital staff said they did not have high hopes of ever seeing their two patients recover.
But after weeks of treatment - involving expert advice from the nearby Porton Down research facility - Yulia and then Sergei were eventually discharged to continue their recovery at an undisclosed address.
The series of interviews with Newsnight marks the first time that staff at the hospital have spoken in detail about the event and how they reacted.
The testimonies of the medical staff highlight the vital importance of the decisions made at key times: the speedy arrival in intensive care, the heavy sedation used to limit possible brain damage, and the importance of advice, tests and treatments suggested by the Porton Down experts.
When the Skripals were found, an opioid overdose was suspected.
"We were just told that there were two patients down in the emergency department who were critically unwell and they would be coming up to the unit," recalled ward sister Ms Clark.
But when police became aware of Mr Skripal's former career as a Russian spy, they told the hospital and discussed the possibility that he may have been the victim of a targeted attack.
A major incident was declared at the hospital and police moved in to protect the Skripals.
"I spoke to the nurse in charge," recalled Dr Duncan Murray, the hospital's senior intensive care consultant, "and it was this conversation I really could never have imagined in my wildest imagination as having with anyone...
"Essentially the story of a known Russian spy having been admitted to hospital in pretty unusual circumstances."
As they continued the treatment, medical staff discarded the earlier theory about opioid poisoning, realising that what they were seeing were symptoms typical of organophosphate, or nerve agent, poisoning.
Dr Stephen Jukes, an intensive care consultant at the hospital, said: "When we first were aware this was a nerve agent, we were expecting them not to survive.
"We would try all our therapies. We would ensure the best clinical care. But all the evidence was there that they would not survive."
Both Skripals were heavily sedated which allowed them to tolerate the intrusive medical equipment they were connected to, but also helped to protect them from brain damage, a possible consequence of nerve agent poisoning.
Over time, the sedation was reduced and the ventilation switched from the mouth to the trachea, as shown by the vivid scar seen on Yulia Skripal's neck in the TV statement she gave after she was released.
Once the patients became more conscious, staff had to carefully consider what they could tell them without prejudicing the police investigation, and decide on the right moment to allow questioning by detectives.
Medical director Dr Christine Blanshard explained: "Those are very difficult decisions, because on the one hand you want to provide reassurance to the patients that they are safe and they are being looked after, and on the other hand you don't want to give them information that might cause difficulties with subsequent police interviews."
It was the doctors and nurses that, out of concern for their patients, insisted that international inspectors obtain a court order before they would be allowed to take blood samples from the Skripals.
Dr Jukes explained: "These are vulnerable patients, they needed some form of advocate and without a court order we could not allow things to happen to them without their consent."
Once the Skripals were stable and able to speak, the key concern for medical staff was how their production of the key enzyme acetylcholinesterase - needed to re-establish their normal body functions - could be stimulated.
The body will do this naturally after nerve agent poisoning, but the process can take many months.
In trying combinations of drugs, Dr Murray says the hospital received input from "international experts", some of them from Porton Down.
The laboratory, internationally known for its chemical weapons expertise, processed tests and offered advice on the best therapies.
New approaches to well-known treatments were tried. Dr Jukes said that the speed of the Skripals' recovery came as a very pleasant surprise that he cannot entirely explain.
Yulia was eventually discharged from Salisbury District Hospital on 9 April - and last week made a statement thanking the hospital. Her father's departure from the hospital was announced on 18 May.
Dr Murray said: "The vast majority of the improvement and the success... were attributable to the very good generic, basic critical care."
He also praised the "excellent teamwork by the doctors, fantastic care and dedication by our nurses".
Inevitably, there will be longer term questions about the Skripals' health.
Dr Blanshard said they would need continuing support, noting: "We have a total world experience of treating three patients for the effects of Novichok poisoning and I think it's safe to say that we're still learning."
Watch the full report here on BBC Newsnight