Oh my God, look at that cardigan. I can’t help gasping aloud. That is stunning. It’s longline, in what seems to be grey cashmere, with an oversized, neon-pink zipper, all the way up the front and the back. It’s gorgeous.

‘So now we’ll rest for a moment …’ Kai is concentrating on his screen. ‘You’re doing great so far.’

The treadmill slows, but I barely notice. I’m feeling stabs of alarm. A pair of passing girls has seen the rail and fallen on it in delight. I can hear them exclaiming with glee, showing clothes to each other and dumping them in their baskets. They’re taking everything! I don’t believe it. The sale of the century is going on, ten yards away, and I’m stuck on this stupid treadmill. As long as they don’t see the cardigan. I will them silently: Don’t look at the cardigan …

‘OK, this is strange.’ Kai is frowning at his screen again. ‘Let’s pause the test.’

‘Actually, I need to leave,’ I say breathlessly, grabbing my handbag and shopping basket. ‘Thanks. If I need a heart monitor I’ll definitely get this one, but I must go …’

‘Rebecca, have you ever been diagnosed with arrhythmia? Heart disorder? Anything like that?’

‘No.’ I’m stopped in my tracks. ‘Why? Have you picked something up?’

Is he joking? No. His face is serious. He isn’t joking. I’m gripped with fright. What have I got? Oh my God, I’ll be in the Daily Mail health pages. My one-in-a-million heart condition was picked up in a simple store exercise test. Shopping saved my life, says Rebecca Brandon—

‘Your heart response wasn’t typical. It spiked, but not at the moments I was expecting. For example, it spiked just now when you were resting.’

‘Oh,’ I say anxiously. ‘Is that bad?’

‘Not necessarily. It would depend on a lot of things. Your general heart health, your cardio fitness …’

As he’s talking, my eye wanders over to the sale rack again, and to my horror I see that one of the girls has picked up my cardigan. No! Noooo! Put it down!

‘It’s happened again!’ says Kai in sudden animation, and points at the screen. ‘Do you see? Your heart rate rocketed!’

I look at Kai, and at the screen, and then at the cardigan with the neon-pink zip, and it all falls into place. Oh God, is that why my heart rate zoomed up?

This is so embarrassing. Stupid dumb heart. I can feel myself blushing bright red and I hastily look away from Kai.

‘Well!’ I say in flustered tones. ‘I have no idea why that happened. None! Just one of those mysteries. Mysteries of the heart. Ha ha!’

‘Oh. OK.’ Kai’s expression snaps as though in recognition. ‘Ooo-kay. I think I get it. I’ve seen this a couple times.’

‘Seen what?’

‘OK, this is a little awkward …’ He flashes me a perfect smile. ‘It was physical attraction to me, right? You don’t need to be uncomfortable. It’s normal. It’s why I had to give up personal training. The clients became … I don’t know, would you say “infatuated”?’ He glances complacently at himself in the mirror. ‘You looked at me and your response was beyond your control. Am I right?’