Waking with a start, she was just in time to see they were leaving Oakwood station. She swore under her breath because she had missed her stop. Feeling sweaty and slightly sick, she glanced around. In an old-style Piccadilly line underground train, there was no easy way to move away from the only other passenger in her carriage. With one more stop before they reached the end of the line, it wasn't worth the effort of yanking open the external doors between carriages. Instead, she sat perfectly still, trying to ignore him.

Every time her eyes flicked over to him, he was staring at her. She was drunk enough to want to leap to her feet and shout at him, 'What the fuck are you staring at, you fucking weirdo?', sober enough to resist the temptation. For all she knew, he might react violently. He had a mop of greasy dreadlocks, and his mouth hung slack beneath his wildly staring eyes. It was impossible to tell if his pupils were dilated, but there was definitely something demented about his expression.

Unnerved, she pulled her hood up and kept her eyes on the filthy floor of the carriage. Without looking at him, she was aware of his presence, every muscle tensed to resist if he approached her. She wanted to close her eyes and drift off to sleep again, but she didn't dare relax her vigilance. In a few minutes they would reach the end of the line. She willed the train to move quickly, hoping there would be other people around when they arrived.

To her dismay, the train juddered to a halt before they reached the station. Every second she sat opposite the stranger seemed to stretch out as though time had become elastic. The air in the carriage felt so stuffy, she thought she would throw up. Sick and frightened, she struggled not to burst into tears. She was too old for this. It wasn't as if she had even enjoyed the evening. After ten years of London clubbing, she was disillusioned with her pursuit of meaningless fun. There must be more to life than frenetic dancing, shagging strangers, and throwing up in gutters.

And now this.

The stranger stirred. 'We're not moving,' he said.

She froze. Out of the corner of her eye she could see him leering at her.

'Don't be upset,' he went on, his words slurring into each other. 'There's nothing to be upset about. Now we get to spend more time together.'

A thrill of terror ran down her spine. This was it. He was going to attack her. She wondered if her rape alarm would deter him. It was deafening, but with no one else around to hear it, the shrill sound would be pointless. As she glanced around for the emergency cord, the train jolted and moved again.

She fished in her bag for her Oyster card and clutched it, so she would be able to leave the station as quickly as possible. If she was fast enough, she would be out in the street before he could follow her. She checked her hood was up and sat on the edge of her seat. As the train drew into the station, she leapt up and dashed to the door.

Without looking back, she could sense the other passenger was close behind her as the train left. She smelt his stale breath when he spoke.

'You in a hurry?' he asked softly.

She didn't turn round. It was best not to answer. He might think she hadn't heard him.

'I asked you a question, bitch.'

A hand gripped her upper arm so suddenly it made her yelp. Biting her lower lip, she spun round, lashing out in terror. As she yanked her arm out of his grasp, her elbow hit the side of his chest. Struggling to cling on to her, he lost his footing. She staggered back and reached out, leaning one hand on the cold wall of the tunnel. Before she had recovered her balance he fell, arms flailing, eyes glaring wildly as he disappeared over the edge of the platform onto the rails below. There was a sharp crack followed by a dull thud and a faint wheezing.

With a shudder, she craned her neck and peered over onto the rails where the man lay, twitching and moaning. He appeared to be having a seizure of some sort. Drawing back, she hurried towards the exit, forcing herself not to break into a run.

At that time of night the station was deserted. For a terrifying instant she thought her Oyster card hadn't registered. But the barrier slid open and she was through.

Outside, the street was empty. In desperation she looked around for a taxi. There was nothing else for it. She had to get away from there. Pulling out her phone, she called her father.

'What are you doing, calling me in the middle of the night? Do you know what time it is?'

'Dad, I need your help.' She hated herself for saying it.

'What?'

'I fell asleep on the train. Can you pick me up? Only ...' she hesitated to mention the weirdo.

'Is everything all right?' her father asked.

'Yes, everything's fine,' she lied. 'I can take care of myself. But I can't see any taxis here and I need a lift home.'

Taking a deep breath, she tried to calm down. As her panic subsided, she realised that she could be in serious trouble. Her father wouldn't turn up for about half an hour, maybe more. In that time, the weirdo might recover or, if he was dead, his body could be discovered. Either way, she wasn't keen to risk being raped or else dragged into a police enquiry. As she vacillated, she checked on her phone and found a night bus that ran from Cockfosters. The next one was due in just over five minutes.

She was on the point of calling her father. Thinking better of her impulse, she stuffed her phone back in her bag. Let him worry about her. It would serve him right. Smiling to herself, she set off for the bus stop.

Geraldine wanted to be alone on her birthday. It wasn't her age that was making her miserable, although she was hardly pleased to be turning forty. The reason she was preoccupied was that her mother was going to be cremated that week. So although she had reached a significant birthday, she didn't feel like celebrating. She hadn't discussed her feelings with anyone.

'You can't change decade without getting hammered!' Sam insisted, her short spiky blonde hair sticking up on top of her head as though to emphasise her indignation. 'Just because you're a detective inspector, and getting on a bit, doesn't mean you have to be all stuffy and boring.'

Geraldine couldn't help laughing at her young detective sergeant. 'Well, thanks for reminding me that I'm so much older than you, and getting older by the minute. I'm not in my twenties any more.' She didn't add that partying was the last thing on her mind. 'But seriously, Sam, don't tell everyone. I don't want any fuss.'

'Aren't we even going out for a drink? We don't have to make a huge deal out of it. We can go out just the two of us.'

Geraldine smiled. She wasn't close to many of her colleagues. Although she knew that Sam socialised with a lot of their fellow officers, nevertheless she was gratified by her sergeant's friendship.

'I can't,' she said. 'I'm going to see my sister.'

That was not an out and out lie. Geraldine had arranged to visit her adopted sister, but not until the weekend.

'Not even one drink?'

Geraldine shook her head. 'Not even one. I'm not as young as you.'

With a guilty twinge she remembered the bottle of wine she was planning to open at home that evening after work.

'Are you trying to tell me the fun ends once you quit your twenties?' Geraldine smiled at her friend's daft grimace. 'I can't remember back that far.'

'If that's the case, I need to pack in as much fun as I can, while I still can. Time's running out for me. I'll be thirty in a couple of years so I need to party now, even if I won't remember it when I'm old. Older,' she added quickly.

Geraldine laughed. 'Imagine how I feel.'

'Look, fair enough you've arranged to spend this evening with your family, but we must go out at the weekend and celebrate. You can't deprive me of this chance to go out on the town. I don't have much longer to go before I'm thirty and then what? Will I really have to grow up and be sensible all the time? Bloody hell. You had to blurt it out, didn't you? And there I was, thinking the fun would never end. Another ten years, and I'll be sipping cocoa at home in the evening, and in bed by nine. You had to tell me, didn't you?' She heaved an exaggerated sigh and Geraldine grinned.

When Sam left, Geraldine turned to her screen, but she was too dejected about her mother to feel aggrieved by her latest budget cut. What would once have started her ranting no longer seemed important. She was growing older. One day she would end her life among strangers, as her mother had done. Pulling herself up short for allowing such negative thoughts to cloud her mind, she turned her attention back to her screen. Whatever else might be happening in her life, her job mattered. As a detective inspector working in serious crime, investigating murder cases, she couldn't allow her personal problems to affect her focus, even for a moment.

Sam called by Geraldine's office at the end of the day.

'Still here?' she asked, looking slightly put out. 'I thought you were off to see your sister this evening?'

Geraldine did her best to conceal her irritation. It felt as though Sam was checking up on her. At the same time, she didn't want to be caught out in a fib.

'Oh, is that the time?' she said, instead of answering directly. 'I'd better be off. Thanks, Sam.'

Quickly closing down her screen, she grabbed her bag, and left the building with Sam at her side.

'Have a good evening,' Sam called out as they parted in the car park. 'And don't forget I owe you a drink.'

'Only one?'

'Now, now, remember you have to be careful at your age.'

At home, Geraldine poured herself a generous glass of wine before taking her iPad out of her bag. She hadn't yet finished checking her budget. Juggling the figures, she tried not to imagine what Sam would say if she could see her now.

When her phone rang, she almost didn't answer, assuming Sam was calling to find out if she had changed her mind. There was still time to go out drinking. Glancing at the call screening, she was pleased to see the name. She had worked with Ian Peterson in Kent before her relocation to London. They had remained friends, and kept in touch even after he had moved away to York. Surprised and pleased that he had remembered her birthday, she picked up her phone.

'Hi. How are you?'

Ian was one of Geraldine's few good friends, but he wasn't calling to wish her a happy birthday. He had called to talk about his marital problems. When he finally got round to asking how she was, she muttered that she was fine. After she hung up, she was overcome by regret that she hadn't been honest with him. He was her closest friend, apart from Sam. Working together led to a kind of bond she had not experienced with anyone else. She had always been able to talk freely with him, but he was preoccupied by his own problems and it wasn't fair to burden him with hers. Besides, his situation could be put right. His wife was alive. Nothing could be done to alleviate Geraldine's misery. With her mother dead, she felt isolated in her grief. On her fortieth birthday, an occasion most people would celebrate with friends or family, she had never felt more alone.

She stared at one glass on the table beside an open bottle of red wine. She was used to being on her own. It didn't normally bother her. In fact, as a rule, it suited her. Occasional bouts of loneliness were a price she was willing to pay for her independence. But this evening her thoughts were darting around in confusion. The following morning she was going to her mother's funeral. Working with the deaths of strangers every day had not prepared her to deal with her own grief.

There had been no chance of him falling asleep until he heard the front door close, telling him that his daughter was home. The last train left from town at around midnight, so she should have been back by now. He had tried to relax, listening out for any sound from downstairs. Five minutes had passed. And another five minutes. In the darkness, time had moved slowly.

It had been gone half past twelve when his phone had rung.

'Dad, thank goodness you're still up. I fell asleep on the train.

'Where are you?'

Beth was at Cockfosters station, about ten miles away. It was the end of the line. He glanced at his watch. At that time of night it might only take him twenty minutes to drive there.

'The station's deserted, and I don't know what to do.'

She had known exactly what to do. She had called him.

'She's twenty-seven,' his ex-wife would say if she knew what had happened. 'She's an adult. Stop running after her. Let her find her own way home. What would she do if you weren't there? She managed all right by herself when we used to go away. It's not healthy to be so obsessed with her. You have to let her live her own life.'

His ex-wife accused him of wanting to keep Beth dependent on him, but it was easy for her to be harsh. Beth wasn't her daughter. He wondered if Veronica was right, and his overprotectiveness was to blame for Beth turning into such a wild teenager. Only six when her mother had died, she had become withdrawn. When Daniel remarried, he had hoped her stepmother would encourage her to feel more settled. Hitting puberty, Beth had flipped to the opposite extreme. Veronica and he had spent years arguing about his daughter's unruly behaviour, but she had grown out of it in the end. She had finally landed herself a job with prospects of a kind.

'It's only a job, dad. There's no need to go overboard.'

'Stick with it and you could end up managing the shop.'

He climbed out of bed, feeling his way in the dark.

Beth sounded slightly hysterical. 'Can you come and get me? I wouldn't ask, only it's late, and I'm outside and there aren't any taxis. There's a man in a van, watching me. Please come, dad.'

Pulling on pants and jeans under his pyjama top, he hurried downstairs. He should have told Beth to go back inside the station and call the police if she felt threatened, although they were unlikely to turn up before him. Fumbling with the phone as he drove off, he called her back to reassure her he was on his way, but there was no answer. He put his foot down. If he was pulled over for speeding, so much the better. The patrol car could drive to Cockfosters station with him.

Although the streets were not exactly busy at that time of night, there were still a surprising number of cars on the road. As he drove, he calmed down. He realised Beth had exaggerated the potential danger of her situation to make sure he went to pick her up. He should have known better than to worry. She could manipulate him so easily. There was no reason why she couldn't stay sober and leave her own car at the station when she went out. He had given her a nice motor he had done up himself at the garage. But she insisted on going out late, drinking and goodness knows what else besides, and then expected him to be on tap to pick her up whenever she needed a lift. Irritated, he rehearsed what he was going to say. Her stepmother was right. Beth was old enough to know better, too old to be causing him this kind of stress in the middle of the night.

'How could you fall asleep on the train at this time of night? You knew how late it was.'

Yet he was pleased she had chosen the safest option, and knew he would say nothing that might discourage her from calling him if she was stranded again. All that mattered was that she was safe. He could easily catch up on a few hours' missed sleep.

A battered black Ford Transit van was driving away from the station as Daniel pulled up. As it passed, he caught sight of a dark-haired man driving, with a blond woman at his side. Too late he remembered Beth had mentioned a van parked at the station. He looked round just in time to catch the registration number. Apart from the van, the road was empty. Annoyed, he climbed out of the car. Beth could at least have run over, grateful to him for turning out at that time of night. Instead she expected him to leave his warm seat to go and look for her. He strode into the station but couldn't see her. He looked around but the station was deserted. He went over to the ticket office and knocked on the window but no one came to his assistance. He hadn't expected to find anyone there.

'Beth?' he called out.

Recovering from his momentary panic, he tried to think logically where she might be. Either she had gone to the toilet, or a late train had arrived, or else she had decided to make her own way home. Perhaps a taxi had turned up. It would be incredibly selfish of her to have summoned him, only to make her way home independently, but he wouldn't put that past her. She might have thought she could get home before he left. It would have been a nice surprise if she had.