The thing about driving to Schleswig-Holstein with two children, a dog, and a boot packed to the gunwales is that you convince yourself you've thought of everything. Sat nav programmed, snacks distributed, loo breaks timed to military precision. What I had not accounted for was my own spectacular gift for misreading a booking confirmation.

We'd been on the road from Hamburg for the best part of three hours, the A7 giving way to smaller roads, then narrower ones still, until we were threading through flat green countryside with the Baltic somewhere just ahead. The children had reached that dangerous stage of boredom where they start asking philosophical questions. "If you could only eat one cheese forever," my daughter said, "would it still be called cheese?" The dog had been sick in a carrier bag. We were all ready to be somewhere else.

I pulled up to the OstseeResort Olpenitz with a genuine sense of triumph. There it was, the Leuchtturm, a proper lighthouse-style holiday home rising up from the coastal development, red and white and improbably cheerful against the grey-blue sky. I found our parking spot, wrestled the cases out, and marched up to the door with the key code clutched in my hand. It did not work. I tried again. Nothing. The dog, sensing weakness, began to bark at a seagull.

It was my wife who spotted it, peering over my shoulder at the confirmation email I'd been waving about. "Love," she said, in that particular tone. "That's next week's date."

I stood there on the doorstep of a lighthouse I had no right to enter, clutching my non-functional code, while my son helpfully observed that I was "going a bit purple." The dog barked again. A woman in the neighbouring property peered out, then tactfully withdrew.

The next twenty minutes involved a phone call of such profound awkwardness that I can still feel it physically. The letting agency, it turned out, were based somewhere with excellent mobile reception and apparently endless patience. They found us a different property for the night, a regular cottage round the corner, and promised the lighthouse would be ours from tomorrow. I thanked them approximately fourteen times and hung up with the hollow gratitude of the massively inconvenienced.

The cottage was fine. More than fine, really, with its little terrace and view of the water. We had fish and chips from a takeaway in Kappeln, ten minutes up the road, and sat outside wrapped in blankets while the children ran about with the dog until all three were muddy and exhausted. My daughter found a crab shell on the little beach and carried it about like a treasure. My son fell asleep at the table with his head on my arm.

Lying in the unfamiliar bed that night, listening to unfamiliar creaks, I found myself unexpectedly content. The mishap had stripped away any notion of a perfect holiday, which was somehow a relief. We'd been messy and disorganised and slightly ridiculous, and here we were anyway, full of mediocre chips, watching the light fade over the Schlei.

The next morning we moved into the Leuchtturm properly, and it was everything we'd hoped, spiral staircase and all. But that first evening, the chaos of it, the sitting together in the cold with our takeaway and our tired dog, that was the bit that stayed. Sometimes the wrong door leads you somewhere better, even if you do have to go a bit purple first.