Around us London was shrill and heaving, even though it was two a.m. We paused for Lily to take joint selfies of us in front of a theatre, a Chinese sign and a man dressed as a large bear (apparently every event had to be marked by photographic evidence), then wove our way through crowded streets in search of a night bus, past the late-night kebab shops and the bellowing drunks, the pimps and the gaggles of screeching girls. My hip was throbbing badly, and sweat was cooling unpleasantly under my damp clothes, but I still felt energized, as if I had been snapped back on.

‘God knows how we’re going to get home,’ Lily said cheerfully.

And then I heard the shout.

‘Lou!’ There was Sam, leaning out of the driver’s window of an ambulance. As I lifted my hand in response, he pulled the truck across the road in a giant U-turn. ‘Where you headed?’

‘Home. If we can ever find a bus.’

‘Hop in. Go on. I won’t tell if you won’t. We’re just finishing our shift.’ He looked at the woman beside him. ‘Ah come on, Don. She’s a patient. Broken hip. Can’t leave her to walk home.’

Lily was delighted by this unexpected turn of events. And then the rear door opened and the woman, in a paramedic uniform, eyes rolling, was shepherding us in. ‘You’re going to get us sacked, Sam,’ she said, and motioned for us to sit down on the gurney. ‘Hiya. I’m Donna. Oh, no – I do remember you. The one who …’

‘… fell off a building. Yup.’

Lily pulled me to her for an ‘ambulance selfie’ and I tried not to look as Donna rolled her eyes again.

‘So where have you been?’ Sam called through to the rear.

‘Dancing,’ said Lily. ‘I’ve been trying to persuade Louisa to be less of a boring old fart. Can we put the siren on?’

‘Nope. Where’d you go? That’s from another boring old fart, by the way. I won’t have a clue whatever you say.’

‘The Twenty-two,’ said Lily. ‘Down the back of Tottenham Court Road?’

‘That’s where we had the emergency tracheotomy, Sam.’

‘I remember. You look like you’ve had a good night.’ He met my eye in the mirror and I coloured a little. I was suddenly glad to have been out dancing. It made me seem like I might be someone else altogether. Not just a tragic airport barmaid whose idea of a night out was falling off a roof.

‘It was great,’ I said, beaming.

Then he looked down at the computer screen on the dashboard. ‘Oh, great. Got a Green One over at Spencer’s.’

‘But we’re headed back in,’ said Donna. ‘Why does Lennie always do this to us? That man’s a sadist.’

‘No one else available.’

‘What’s going on?’

‘A job’s come up. I might have to drop you. It’s not far from yours, though. Okay?’

‘Spencer’s,’ said Donna, and let out a deep sigh. ‘Oh, marvellous. Hold on tight, girls.’

The siren went on. And we were off, lurching through the London traffic with the blue light screaming above our head, Lily squealing with delight.

On any given week-night, Donna told us, as we clutched the handrails, the station would get calls from Spencer’s, summoned to fix those who hadn’t made it upright to closing time, or to stitch up the faces of young men for whom six pints in an evening left them combative and without any accompanying sense. ‘These youngsters should be feeling great about life, but instead they’re just knocking themselves out with every spare pound they earn. Every bloody week.’

We were there in minutes, the ambulance slowing outside to avoid the drunks spilling out onto the pavement. The signs in Spencer’s nightclub’s smoked windows advertised ‘Free drinks for girls before 10 p.m.’ Despite the stag and hen nights, the catcalling and gaudy clothes, the packed streets of the drinking zone had less of a carnival atmosphere than something tense and explosive. I found myself gazing out of the window warily.

Sam opened the rear doors and picked up his bag. ‘Stay in the rig,’ he said, and climbed out.

A police officer headed over to him, muttered something, and we watched as they walked over to a young man who was sitting in the gutter, blood streaming from a wound to his temple. Sam squatted beside him, while the officer attempted to keep back the drunken gawkers, the ‘helpful’ friends, the wailing girlfriends. He seemed to be surrounded by a bunch of well-dressed extras from The Walking Dead, swaying mindlessly and grunting, occasionally bloodied and toppling.

‘I hate these jobs,’ said Donna, checking briskly through her pack of plastic-wrapped medical supplies as we watched. ‘Give me a woman in labour or a nice old granny with cardiomyopathy any day. Oh, flipping heck, he’s off.’

Sam was tilting the young lad’s face to examine it when another boy, his hair thick with gel and the collar of his shirt soaked in blood, grabbed at his shoulder. ‘Oi! I need to go in the ambulance!’

Sam turned slowly towards the young drunk, who was spraying blood and saliva as he spoke. ‘Back away now, mate. All right? Let me do my job.’

Drink had made the boy stupid. He glanced at his mates, and then he was in Sam’s face, snarling, ‘Don’t you tell me to back away.’

Sam ignored him, and continued attending to the other boy’s face.

‘Hey! Hey you! I need to get to the hospital.’ He pushed Sam’s shoulder. ‘Hey!’

Sam stayed crouched for a moment, very still. Then he straightened slowly, and turned, so that he was nose to nose with the drunk. ‘I’ll explain something in terms you might be able to understand, son. You’re not getting in the truck, okay? That’s it. So save your energy, go finish your night with your mates, put a bit of ice on it, and see your GP in the morning.’

‘You don’t get to tell me nothing. I pay your wages. My effing nose is broke.’

As Sam gazed steadily back at him, the boy swung out a hand and pushed at Sam’s chest. Sam looked down at it.

‘Uh-oh,’ said Donna, beside me.

Sam’s voice, when it emerged, was a growl: ‘Okay. I’m warning you now –’

‘You don’t warn me!’ The boy’s face was scornful. ‘You don’t warn me! Who do you think you are?’

Donna was out of the truck and jogging towards a cop. She murmured something in his ear and I saw them both look over. Donna’s face was pleading. The boy was still yelling and swearing, now pushing at Sam’s chest. ‘So you sort me out before you deal with that wanker.’