I had not been wrong about the Evian lady’s feelings towards me. She had been helpful, she had done her duty, she had answered the madwoman’s questions. Our relationship was now completely terminated. But she had provided more clues. Just when I was about to give up the trail, I was back in business.

So the letter-writer was likely to be a Parisian, since the bottles were ‘intended for the metro’. As she was rushing back from work one day, through the crowded tunnels, the unknown mother was stopped in her tracks by the sight of a water dispenser filled with beautiful tear-shaped bottles. They seemed to beckon to her, and speak through the grime of urban travel about distant waves and sea spray. She scrabbled desperately in her bag for some coins. She would use the bottle to send a message . . .

But . . . Before I leapt to conclusions – maybe there were metros in other large French towns? If the factory knows exactly when the bottle was produced, why can’t they track down exactly to which metro it went? But the Evian lady was so clearly fed up with the whole subject and with me that I dared not write again. Instead I sent out a desperate query email to five French friends.

My friends started to reply:

Are you sure she said ‘LA metro’? If she did, that means metropolitan France, in other words it was not intended for export or for anywhere beyond the mainland.

A short while later a second friend replied:

Bad luck, there are metros throughout France.

A friend whose husband is a French historian specializing in the First World War was the third to answer my email. Her husband’s books deal with the historic relationships between mothers and their children: grieving mothers whose sons were killed on the battlefields, children in battle and the conflict between maternal affection and the revulsion that raped women feel towards the resulting offspring. This friend wrote:

Sadly there are many Metros. Check out their website.

I followed the hypertext link she had included on her email to discover that Metro is the fifth largest world distribution group, with Walmart in first place. Metro runs Cash & Carry-type stores across northern France. The largest – 16,000 square metres – is at Lomme/Lille, the next at Rouen. Along the coast itself there are two stores, at Caën and at Calais. This was a whole new – and unwelcome – linguistic development.

‘How do you know it is not the underground kind of metro?’ I queried. The reply was firm: ‘“Grandes surfaces” [large areas] in Evian’s email means supermarkets,’ she wrote. ‘And there is no capital letter on Metro, because I think it is a diminutive of “la société métro” – the metro company, and perhaps that is also why it is used in the feminine.’

The image of the letter-writer stopping to buy a bottle of water in the crowded Paris underground and suddenly being overwhelmed by the urge to write a letter in a bottle evaporated.