It began with a conversation between a foreign correspondent who loves ballads, and his neighbour, a legend of the British folk music scene.
The result was Ralph McTell agreeing to write a new verse of his legendary hit Streets of London - something he'd always previously refused to do.
First recorded in 1969, the song at one point sold 90,000 copies a day and has been covered by more than 200 artists. It also won Ralph an Ivor Novello award for best song and continues to feature in folk music's "best of" playlists.
'This is no dress rehearsal'
Ralph is a neighbour and also one of the kindest men I know. Since I was a teenager I have loved his bittersweet songs of the heart and acute social observation.
Like most of the population, Ralph, aged 75, is observing the lockdown in his London home. As an avid follower of news he watched, appalled, as the Covid-19 crisis swept the world.
"This is of biblical proportions, this catastrophe," he told me. "And each day that goes by there is the realisation that this is no dress rehearsal, this is actually going on right now and there is nothing we can do about it, except try and follow the basic rules."
Born into a working class family in Croydon, south London, at the end of World War Two, Ralph left home and joined the army aged 15. His social conscience was forged in a post-war world circumscribed by poverty. It is not a pose.
With its focus on the homeless and imagery of lonely figures moving through an uncaring world, Streets of London resonates powerfully now as thousands of rough sleepers across Britain are seeking a place of safety.
Chatting on the phone, I told Ralph I had been filming with homeless people in London and of how they were searching for a safe place to self isolate.
I spoke of a young woman called Blue, aged 29, who I'd met living under a railway bridge and how fearful she was that she would be arrested and put into isolation.
"What would you write now if there was to be another verse to the song?" I asked.
Changing the song was something he'd always resisted, he said. It was written when he was 22 and belonged to a particular time. But this was an extraordinary moment in history. "Give me a chance to think and try and write something."
This new verse was the moving result:
In shop doorways, under bridges, in all our towns and cities
You can glimpse the makeshift bedding from the corner of your eye
Remember what you're seeing barely hides a human being
We're all in this together, brother, sister, you and I.
Ralph is an optimist. In recent daily encounters he has detected a new mood of community.
In his area of west London, it has manifested itself in warmer greetings and observing the rules of social distancing. He is aware of the paradox that what pushes us physically apart might bring us closer.
"I've got a little dog and took her for a walk yesterday. And I noticed people as they're getting closer to each other they just sort of smile and move apart and I thought, 'Ah the message is going in at last. Yes I think we're all going to be different after this.'"
Like his musical colleagues, Ralph is unable to perform in front of crowds for as long as Covid-19 remains a major public health hazard.
But his great song - with its new verse - is a powerful appeal to our better natures in these fearful times.