OK. Don’t panic. Don’t panic.

I’ll escape from this. Of course I will. It’s not like I’ll be trapped here in this hideous confined space, with no hope of release, forever … is it?

As calmly as possible, I assess the situation. My ribs are squashed so that I can hardly breathe, and my left arm is pinned behind me. Whoever constructed this “restraining fabric” knew what they were doing. My right arm is also pinned, at an awkward angle. If I try to reach my hands forward, the “restraining fabric” bites into my wrists. I’m stuck. I’m powerless.

My face is reflected, ashen, in the mirror. My eyes are wide and desperate. My arms are crisscrossed with black shiny bands. Is one of them supposed to be a shoulder strap? Does that webbing stuff go round the waist?

Oh God. I should never ever have tried on the size 4.

“How are you doing in there?” It’s Mindy, the sales assistant, calling from outside the cubicle curtain, and I start in alarm. Mindy is tall and rangy, with muscled thighs that start three inches apart. She looks like she probably runs up a mountain every day and doesn’t even know what a KitKat is.

She’s asked three times how I’m doing, and each time I’ve just called out shrilly, “Great, thanks!” But I’m getting desperate. I’ve been struggling with this “Athletic Shaping All-in-One” for ten minutes. I can’t keep putting her off forever.

“Amazing fabric, right?” says Mindy enthusiastically. “It has three times the restraining power of normal spandex. You totally lose a size, right?”

Maybe I have, but I’ve also lost half my lung capacity.

“Are you doing OK with the straps?” comes Mindy’s voice. “You want me to come in the fitting room and help you adjust them?”

Come in the fitting room? There’s no way I’m letting a tall, tanned, sporty Angeleno come in here and see my cellulite.

“No, it’s fine, thanks!” I squawk.

“You need some help getting it off?” she tries again. “Some of our customers find it tricky the first time.”

I have a hideous vision of me gripping the counter and Mindy trying to haul the All-in-One off me while we both pant and sweat with the effort and Mindy secretly thinks, I knew all British girls were heifers.

No way. Not in a million years. There’s only one solution left. I’ll have to buy it. Whatever it costs.

I give an almighty wrench and manage to snap two of the straps up onto my shoulders. That’s better. I look like a chicken trussed up in black Lycra, but at least I can move my arms. As soon as I get back to the hotel room, I’ll cut the whole thing off myself with a pair of nail scissors and dispose of the remains in a public bin so Luke doesn’t find them and say What’s this? or You mean you bought it even though you knew it didn’t fit? or something else really annoying.

Luke is my husband, and he’s the reason I’m standing in a sports-apparel shop in L.A. We’re moving out to Los Angeles as soon as possible because of his work, and we’re here on an urgent house-hunting trip. That’s our focus this week: Real estate. Houses. Gardens. Rental agreements. Very much so. I’ve only popped to Rodeo Drive very, very quickly between house appointments.

Well, OK. The truth is, I canceled a house appointment to come to Rodeo Drive. But I had to. I have a genuine reason for needing to buy some emergency running clothes, which is that I’m running in a race tomorrow afternoon. A real race! Me!

I reach for my clothes, grab my bag, and walk stiffly out of the cubicle to see Mindy hovering nearby.

“Wow!” Her voice is bright but her eyes are shocked. “You look …” She coughs. “Awesome. It’s not too … tight?”

“No, it’s perfect,” I say, attempting a carefree smile. “I’ll take it.”

“Great!” She can barely hide her astonishment. “So, if you want to take it off, I’ll scan it for you.…”

“Actually, I’ll wear it.” I try to sound casual. “Might as well. Can you put my clothes in a bag?”

“Right,” says Mindy. There’s quite a long pause. “You’re sure you don’t want to try the size six?”

“No! Size four is perfect! Really comfy!”

“OK,” says Mindy after a silence. “Of course. That’ll be eighty-three dollars.” She scans the bar code on the tag hanging from my neck, and I reach for my credit card. “So, you’re into athletics?”

“Actually, I’m running in the Ten Miler tomorrow.”

“No way!” She looks up, impressed, and I try to appear nonchalant and modest. The Ten Miler isn’t just any old running race. It’s the race. It’s held every year in L.A., and loads of high-profile celebrities run it, and they even cover it on E! And I’m in it!