Le P’tit Pinson, tucked into the corner of the Rue des Faux-Monnayeurs, is an old-style café from the dingy days of Montmartre, dark and smoky and panelled in layers of grease and nicotine. Its owner is Laurent Pinson, a sixty-five-year-old native Parisian with an aggressive moustache and poor personal hygiene. Like Laurent himself, the café’s appeal is generally limited to the older generation – who appreciate its modest pricing and its plat du jour – and the whimsical like myself, who enjoy its owner’s spectacular rudeness and the extreme politics of its elderly patrons.

Tourists choose the Place du Tertre, with its pretty little cafés and gingham-topped tables along the cobbled lanes. Or the art déco pâtisserie on the lower Butte, with its jewelled array of tarts and confits. Or the English tea-shop on Rue Ramey. But I’m not interested in tourists. I’m interested in that chocolaterie, which I can see quite clearly from across the square. From here I can see who comes and goes, I can count the customers, monitor deliveries and generally acquaint myself with the rhythms of its little life.

The letters I stole on that first day have proved less than useful in practical terms. A stamped invoice dated 20th October, marked PAID IN CASH, from Sogar Fils, a confectionery supplier. But who pays in cash nowadays? An impractical, senseless means of payment – doesn’t this woman have an account? – which leaves me as ignorant as I was before.

The second envelope was a sympathy card for Madame Poussin, signed Thierry, with a kiss. Postmarked London, with a see you soon, and please don’t worry casually appended.

File that away for later use.

The third, on a faded postcard of the Rhône, was even less informative.

Heading north. I’ll drop by if I can.

Signed R, the card was addressed only to Y and A, though the writing was so careless that the Y looked more like a V.

The fourth, junk mail peddling financial services.

Still, I tell myself. There’s time.

‘Hey! It’s you!’ The artist again. I know him now; his name is Jean-Louis, and his friend with the beret is Paupaul. I see them often at Le P’tit Pinson, drinking beer and chatting up the ladies. Fifty euros pays for a pencil sketch – call it ten for the sketch, and forty for the flattery – and they have their spiel down to a fine art. Jean-Louis is a charmer – plain women are particularly susceptible – and it is his persistence, rather than his talent, that holds the secret of his success.

‘I won’t buy it, so don’t waste your time,’ I told him as he opened his pad.

‘Then I’ll sell it to Laurent,’ he said, with a wink. ‘Or maybe I’ll just keep it myself.’