Before doing something really stupid, such as walking out onto a railway track, your well trained police officer is required to make a risk assessment. Proper procedure would have been to call up the BTP and have them send a safety qualified search team who might, or might not, shut the line as a further precaution to allow me and Abigail to go looking for a ghost. The downside of not calling the BTP would be that, should anything happen to Abigail, it would effectively be the end of my career and probably, because her father was an old-fashioned West African patriarch, my life as well.

The downside of calling them would be explaining what I was looking for, and having them laugh at me. Like young men from the dawn of time I decided to choose the risk of death over certain humiliation.

Lesley said we should check the timetables at least.

‘It’s Sunday,’ said Abigail. ‘They’re doing engineering works all day.’

‘How do you know?’ asked Lesley.

‘Because I checked,’ said Abigail. ‘Why did your face fall off?’

‘Because I opened my mouth too wide,’ said Lesley.

‘How do we get down there?’ I asked quickly.

There were council estates built on the cheap railway land either side of the tracks. Behind the 1950s tower block on the north side was a patch of sodden grass, lined with bushes, and behind these a chain-link fence. A kid-sized tunnel through the bushes led to a hole in the fence and the tracks beyond.

We crouched down and followed Abigail through. Lesley sniggered as a couple of wet branches smacked me in the face. She paused to check the hole in the fence.

‘It hasn’t been cut,’ she said. ‘Looks like wear and tear – foxes maybe.’

There was a scattering of damp crisp packets and coke cans that had washed up against the fence line – Lesley pushed them around with the toe of her shoe. ‘The junkies haven’t found this place yet,’ she said. ‘No needles.’ She looked at Abigail. ‘How did you know this was here?’

‘You can see the hole from up on the footbridge.’

Keeping as far from the tracks as we could, we made our way under the footbridge and headed for the concrete mouth of the tunnel under the school. Graffiti covered the walls up to head height. Carefully sprayed balloon letters in faded primary colours overlaid by cruder taggers using anything from spray paints to felt tip pens. Despite a couple of swastikas, I didn’t think that Admiral Dönitz would have been impressed.

It kept the drizzle off our heads, though. There was a piss smell but too acrid to be human – foxes I thought. The flat ceiling, concrete walls and the sheer width that it covered meant it felt more like an abandoned warehouse than a tunnel.

‘Where was it?’ I asked.

‘In the middle where it’s dark,’ said Abigail.

Of course, I thought.