All morning a tune intrudes on my solitary work, the theme from The Great Escape. I cannot shake the blasted thing; du dum, du dum du du dum . . . . On it goes, this worm of a tune, insidious, distracting, joining with the blazing heat to slow me down and tempt me to idleness, until the midday Angelus, with its promise of lunch—perhaps the saumon en papillote—spurs me to finish the job.

‘Can you help me please, Monsieur? I can’t seem to get this door open.’

She calls me as I cross the road into the shade of trees on my way home. The door belongs to the electricity substation, as I assume the plain building to be from the company vans that are often parked there.

‘The key turns, but the door won’t budge.’

It must be her first visit, or at least her first alone. Why has she come? Slight and dark-haired, she wears no ID and carries only a folder and a cloth bag too small for a set of tools or instruments or anything nefarious. Unsure how to question her right to access, I settle for the presumption that saboteurs do not come with keys.

‘I’ll try,’ I say.

In the matter of hefty security doors I have no illusion of competence, but she needs help. My bottom line is to not look foolish, whereas she has already weighed the passing embarrassment of appealing to me against the ridicule she would face if she had to admit—as the youngest person at her office I would guess—‘I couldn’t open the door.’ The laughter would haunt her forever.

The key does indeed turn, clockwise, twice round in a sophisticated lock. Pulling the door and pushing it firmly, then sharply, makes no impression. Counter-clockwise perhaps; push, pull. Still no go. What now?

For a moment I peer around the corner of the building, wondering if the key might fit some other door. Already I must appear daft or desperate.

‘Sorry, I can’t work it, I’m really sorry.’ She is gracious, and I am about to give up when, challenged by the door’s obstinacy and my own failure, I tinker. This is usual for me. Being no mechanic, and lacking substantial experience, I try to solve technical problems from basic principles and, when that fails, tinker.

You know how it is with locks. Sometimes they make you struggle as if you are levering the whole wretched door by means of the key rather than merely retracting a latch or deadbolt. The impeccable mechanism before me, however, responds with so little friction, so softly, that you might say it does it willingly—until it reaches a definite, dead stop. Given that, why do I try an extra twist, vigorous and challenging compared to the ease of the main rotation? Perhaps I fancy that the fitting in the door might be out of line, in contradiction of the lock’s dynamic perfection.

It gives. The lock gives. The key turns less than ten degrees, but deep in the door, something shifts. Surprised, I release the pressure and an opposing force pushes the key back. A spring.

When I first tried the door, its flanges and frame convinced me that it would open outwards. Now as I give the key its firm, extra turn once more, it seems natural to pull. Nothing. Before I release the key, however, without intending to, I nudge the door.

It gives way. It swings on balanced hinges, silent, as easy as our fridge, with no protesting squeal or scrape that you might expect of a difficult door. We look at each other, the young woman and I, sheepish. She pushes the door fully open to reveal heavy duty electrical switchgear, consistent with the impression I had gained of the building.

I say a silly thing, ‘Be careful,’ as if the young woman now stepping inside is going to be anything but wary among all these volts. She has been unable to open the door, I have got lucky, but my absurd caution, which I regret at once, might have spoiled the encounter—had she heard it. I wish her a good day: ‘Bonne journée’. She thanks me and I carry on to lunch. Opening the door has taken a minute.

I escape up the hill; du dum, du dum du du dum . . . .

She will, I bet, say nothing to her colleagues.