The time when sheep trampled their tents at night. The time when Peter got stranded out on the tidal marsh and Erik had to rescue him, crawling on his hands and knees across the mudflats. The unbelievable excitement when they found that first wooden post, proof that the henge actually existed. She remembers the exact sound of Erik's voice as he turned and shouted at them across the incoming tide, 'We've found it!'

She turns to Nelson. 'We were looking for a henge.'

'A henge? Like Stonehenge?'

'Yes. All it means is a circular bank with a ditch around it. Usually with posts inside the circle.'

'I read somewhere that Stonehenge is just a big sundial.

A way of telling the time.'

'Well, we don't know exactly what it was for,' says Ruth, 'but it's safe to say that it involves ritual of some kind.'

Nelson shoots a strange look at her.

'Ritual?'

'Yes, worship, offerings, sacrifices.'

'Sacrifices?' echoes Nelson. He seems genuinely interested now, the faintly condescending note has disappeared from his voice.

'Well, sometimes we find evidence of sacrifices. Pots, spears, animal bones.'

'What about human bones? Do you ever find human bones?'

'Yes, sometimes human bones.'

There is silence and then Nelson says, 'Funny place for one of those henge things, isn't it? Right out to sea.'

'This wasn't sea then. Landscape changes. Only ten thousand years ago this country was still linked to the continent. You could walk from here to Scandinavia.'

'You're joking!'

'No. King's Lynn was once a huge tidal lake. That's what Lynn means. It's the Celtic word for lake.'

Nelson turns to look sceptically at her, causing the car to swerve alarmingly. Ruth wonders if he suspects her of making the whole thing up.

'So if this area wasn't sea, what was it?'

'Flat marshland. We think the henge was on the edge of a marsh.'