'Still seems a funny place to build something like that.'

'Marshland is very important in prehistory,' explains Ruth, 'it's a kind of symbolic landscape. We think that it was important because it's a link between the land and the sea, or between life and death.'

Nelson snorts. 'Come again?'

'Well, marsh isn't dry land and it isn't sea. It's a sort of mixture of both. We know it was important to prehistoric man.'

'How do we know?'

'We've found objects left on the edge of marshes. Votive hoards.'

'Votive?'

'Offerings to the Gods, left at special or sacred places.

And sometimes bodies. Have you heard of bog bodies?

Lindow Man?'

'Might have,' says Nelson cautiously.

'Bodies buried in peat are almost perfectly preserved, but some people think the bodies were buried in the bogs for a purpose. To appease the Gods.'

Nelson shoots her another look but says nothing. They are approaching the Saltmarsh now, driving up from the lower road towards the visitor car park. Notices listing the various birds to be found on the marshes stand around forlornly, battered by the wind. A boarded-up kiosk advertises icecreams, their lurid colours faded now. It seems impossible to imagine people picnicking here, enjoying icecreams in the sun. The place seems made for the wind and the rain.

The car park is empty apart from a solitary police car.

The occupant gets out as they approach and stands there, looking cold and fed up.

'Doctor Ruth Galloway,' Nelson introduces briskly, 'Detective Sergeant Clough.'

DS Clough nods glumly. Ruth gets the impression that hanging about on a windy marshland is not his favourite way of passing the time. Nelson, though, looks positively eager, jogging slightly on the spot like a racehorse in sight of the gallops. He leads the way along a gravel path marked 'Visitor's Trail'. They pass a wooden hide, built on stilts over the marsh. It is empty, apart from some crisp wrappers and an empty can of coke lying on the surrounding platform.