She didn’t say no – which was a good start. I looked at her and showed my palms in supplication. The muscles in her jaw worked, and she sucked the inside of her cheeks. Any decision she was going to make would be as much personal as it would be professional. I’d clearly been through the wringer. The question for her, perhaps, was whether or not I’d deserved it. But despite the sheer weight of her misgivings, her evident ambivalence towards the police, mixed up with a high dose of good old-fashioned curiosity, was getting the better of her.

She nodded.

‘OK, take out your phone and google the FCO.’

‘The what?’

‘The Foreign and Commonwealth Office.’

‘Are you serious?’

‘Yup. Go on. It’s not going to blow up or anything.’

‘No, I mean about my being at risk?’

‘Uh-huh.’ Another pause. ‘But look at it this way: if I am delusional, then all this will add up to,’ I nodded towards her wedding ring, ‘is a good story to tell your husband tonight. Five minutes. That’s all. And then we can all go home,’ I lied.

She shook her head as if being petitioned by a child – or an idiot. ‘Wife,’ she said. ‘I’m married to a woman.’

Nearly two and a half decades of professional people-watching, upon which dozens of life and death decisions had been made, and I still couldn’t work out if women were flirting with me – or just fucking with me.

She fidgeted and tugged at her sleeve, wrestling with her reservations. Then: ‘Oh, sod it!’ She exhaled the words hard. ‘Five minutes, OK. Deal?’

‘Deal.’

Her phone was tucked away in a trouser pocket, hidden beneath her lab coat. She fished it out and unlocked it. ‘I must be bloody mad.’

I kept looking at her phone. She tapped the three letters in with her right thumb, her eyes now flitting between mine and the screen.

‘OK, good,’ I smiled. ‘Click on their website and then scroll down, all the way to the bottom, to the main switchboard number, the one that ends with fifteen hundred.’ She went to speak but stopped herself. ‘You’re going to dial the number,’ I said slowly.

‘Anyone could have memorized that number. That doesn’t prove anything.’

‘Of course,’ I agreed. ‘When you dial it, you’re going to get a recorded message with a menu asking what extension or department you want. Ignore them all and key in star, followed by one-nine-zero-nine and then the hash key. That’s going to put you through to an operator who’s going to be bloody rude. She’ll say, “Embankment”, and then ask you what extension you require. Tell her, “Stirling Lines”.’

‘You’ve got it all worked out, haven’t you? What is this – some special code to sucker unsuspecting civvy girls?’