'Is there any other point to which you would wish to draw my attention?' 'To the curious incident of the dog in the night-time' 'The dog did nothing in the night-time'. 'That was the curious incident', remarked Sherlock Holmes.
That famous exchange between Sherlock Holmes and his sidekick Dr Watson in the classic Sir Arthur Conan Doyle short story 'Silver Blaze', springs readily to mind when one considers the strange silence of Sergei Skripal.
This week, the Times newspaper reported that the British authorities had rejected a claim by Sergei Skripal's niece that the former Russian double agent, who was poisoned with nerve agent in Salisbury on 4th March, could already be dead.
But if Skripal is not dead, then why haven't we heard from him, or seen any recent photograph of him?
There have in fact, been no pictures of him, since 4th March, the day he was poisoned. He's become the 2018 equivalent of H.G. Wells' Invisible Man.
Let's think this through logically, without fear or favour.
Skripal, we were told, was discharged was from Salisbury District hospital on Friday 18th May, over two months on from him being found unconscious, with his daughter Yulia, on a park bench near to the centre of the Wiltshire town.
Five days later, on Wednesday 23rd May, Yulia appeared on video, making a short statement that was filmed in a secret location somewhere in England.
She said: 'I take one day at a time and want to help care for my Dad till his full recovery. In the longer term I hope to return to my country'.
She also said: 'I want to re-iterate what I said in my earlier statement that no one speaks for me, or my father, but ourselves'.
The next we hear from Yulia is in a telephone call to her cousin Vicktoria, which took place on or around 4th July.
In it, she blames her cousin for making 'this public' and says 'I am just asking that no one interferes in this situation, that's all'.
Yulia says that 'no-one' is stopping her returning home to live her life. 'I can do that any day. It's just that I am currently looking after my father and recovering myself'.
The investigative blogger The Blogmire, who has done some really excellent work on the case, surmises that Yulia Skripal did not know that Russia had been blamed when she spoke to her cousin. She had not been told this by the UK authorities.
'Had she been told, she could hardly have blamed her cousin for creating the publicity that is apparently preventing her return', The Blogmire writes.
It's clear also that Yulia doesn't blame Russia for trying to kill her, or else she would not have said that she could return home 'any day'.
Why would she want to go a place where the government/state security services had tried to kill her and her father, even if it was her home country?
Even more interestingly, Viktoria says another call with Yulia took place on 24th July, in which Yulia said 'I finally got the internet, and I read everything. I understood everything. Forgive me'.
In that phone call, to her grandmother on her birthday, Yulia says that she is in London with her father.
She says: "He can't speak because he's got a tracheotomy, that pipe, which will be taken off in three days.
"Now when he speaks with that pipe, his voice is first of all very weak and secondly he makes quite a lot of wheeze."
That would explain why we hadn't heard from Sergei up to then, but one more month has now passed.
Viktoria said that Yulia told her her father would call on his own after the pipe had been removed, but there's been no word from him. Why no updates on his condition?
Another important question we need to ask is: why did the British authorities keep Yulia and presumably Sergei Skripal too, in the dark about them blaming Russia, at least until early July?
Could it be because they knew Russia was not responsible and that they knew that Yulia and Sergei knew that too, because they had a very good idea of who had attacked them?
Let's suppose that someone else was behind the 'attack', to use Yulia's own term.
The exposure of that would be hugely embarrassing for the British government, and indeed for most of the political and media establishment, who decided Russia was guilty even before any kind of criminal investigation could begin.
Not only did Britain expel 23 Russian diplomats, it urged other countries to do the same.
There were even calls for the football World Cup to be taken away from Russia and for Russian media operating lawfully in the UK to be shut down.
Don't forget too that only last week new US sanctions on Russia, imposed because of the Skripal case, came into force.
The Russian claim for compensation, if the accusations are revealed as false, could run into billions of dollars.
Which begs the question: if it wasn't Russia, but some other actor, state or non-state, would we ever be allowed to know?
Surely if Yulia or Sergei agreed with the UK government line that Russia was responsible, the authorities would have done everything to get them in front of a camera, reading a statement to that effect.
Think how that would aid the anti-Russian cause, which the British neoconservative government is so keen to pursue.
The fact that neither Skripal has come out with any such statement, is arguably as significant as Sherlock Holmes's dog that didn't bark in the night time.
As to the claims circulating that Sergei is already dead, a simple short video, or, if that's not possible, a dated photograph, could easily disprove that and end the speculation.
The public needs to know what's going on.
We need to hear from Yulia and Sergei Skripal and their account of what happened on 4th March. We need to see the evidence, as this is a matter of great national and international significance.
Is that really too much to ask for, Mrs May?