hels shoes copy… were the shoes off her feet.

This happened in a café in Amsterdam.

There was giggling. There was mild screeching. There was even, I regret to say, a brief scrabble under the table to facilitate the transfer.

We were in a state of relief and benevolence. Relief, because we had given our first choral performance in Amsterdam. Benevolence, because my friend Helen was recovering from a foot injury. The cast she’d been wearing for weeks had only just come off and the whole area – leg, ankle, foot — was still tender. Standing on a hard floor in a cold church and singing for an hour hadn’t helped. Neither had the long walk to a café after the concert.

By the time we sat down and ordered the first round of drinks Helen’s convalescent foot, laced into a vaguely orthopaedic oxford, was swollen, red and puffy around the ankle. Assessing the damage, it occurred to me that Helen and I could swap shoes. My feet are bigger than hers and I was wearing slip-on ballerinas with padded insoles.

This seemed a brilliant solution.

Did I mention we were a little tipsy?

Sober, it might have occurred to me that Helen’s comfort in a pair of oversized ballerinas was, ipso facto, contingent on my discomfort in footwear a size too small.

Even worse, much worse, Helen’s vaguely orthopaedic oxfords did not match my outfit.

I was wearing a fitted black dress, mid-length, a leather jacket and lacy tights with my black ballerinas. The dress for singing, the jacket for edge, the tights and ballerinas for, well, prettiness. A touch of grace. The vaguely orthopaedic oxfords – chic on Helen – distorted the effect. Wearing them, I went from genteel biker girl to strict KGB operative: Lotte Lenya as Rosa Klebb in From Russia With Love, with her mulish expression and a switchblade embedded in the sole of her brogue.

It was not the look I’d been going for. It was jarring and borderline freakish. This bothered me.

But this was before I discovered the Amsterdam Factor.

The Amsterdam Factor is a phenomenon that creeps up on you, takes you by surprise. It snuck up on me when we left the café and went off in search of culture.

After all, we were in Amsterdam: birthplace of the Dutch Golden Age, capital of the Kingdom of the Netherlands, a port city steeped in history and art, trade and finance.

And the first piece of culture we encountered, the very first one, was the Amsterdam Museum of Prostitution.

This was housed in a tasteful canal-side mansion. There was a dignified plaque by the entrance.

We went in, but we didn’t stay long, just long enough to check out the pictures hanging in the lobby. These were photographs of a few of the museum’s exhibits, the coming attractions, if you will. There were photos of handcuffs and pulley devices, photos of men in partial animal costumes and a few shots of very competent-looking women in masks and thigh boots. What was strange was the overall tone, the ethos of the joint: it was matter of fact — tolerant, casual and dissipated all at the same time. Studying these images, it dawned on me that what I was wearing –vaguely orthopaedic oxfords wedded to a leather jacket and a fitted dress – was absolutely fit for purpose in Amsterdam.

In a city with one of the most jaded sexual palates on earth, the incongruous and jarring is not just the norm, it’s a necessity.

The unaccustomed is actually the customary.

That’s the Amsterdam Factor.

And it’s not just the obvious erotic displays in the red light district, women in underwear gesturing to you from inside lit-up booths: the startling, decadent invitations are everywhere, usually when you least expect them. Making our way from the Rijksmuseum to the Van Gogh Museum, from cultural point A to cultural point B as it were, Helen and I passed a small grocery store. There in the shop window, laid out between a stack of Pringles and a pyramid of Diet Cokes, was a sexual device so complicated, so abundant in possibilities — parts springing from it, holes and gashes cut into it –it seemed to speak to every conceivable carnal taste. The shape of a torso with the bulk of a carton, it was hard to know what to call it.

We Instagrammed it to Helen’s husband.

He texted us right back.

Let’s just call it a kind of chair, he said. An unusual kind of chair.

He was half right. A kind of chair, that would do as a description, but in Amsterdam, there was nothing unusual about it.