‘Sometimes,’ says Nelson cautiously. ‘Ruth… Dr Galloway… and I worked on a case together recently.’

‘That affair on the Saltmarsh?’ asks Max, his eyes wide.

‘Yes,’ says Ruth shortly. ‘DCI Nelson called me in when he found some bones on the marsh.’

‘Turned out to be bloody Stone Age,’ says Nelson.

‘Iron Age,’ corrects Ruth automatically. ‘Actually, Nelson, Max found some human bones today.’

‘Iron Age?’ asks Nelson.

‘Roman, we think. They seem to have been buried under the wall of a house. Come and see.’ She leads them down the bank and towards the earthworks. Close up, Nelson sees that the land is full of these strange mounds and hills, some curving round, some standing alone like large molehills.

‘What are all these bumps?’ he asks Max Grey.

‘We think they’re walls,’ replies Max, his face lighting up in the way that archaeologists have when they are about to bore the pants off you. ‘You know, we think there was a whole settlement here, we’re fairly near the old Roman road but, from the surface, the only signs are some brown lines in the grass, crop marks, that sort of thing.’

Nelson looks back at the smoothly curving bank. He can just about imagine it as a wall but the rest just looks like grass to him.

‘This body, you say it’s under a wall?’

‘Yes. We just dug a trial trench and there it was. We think it’s the wall of a villa, quite a sizeable one, by the looks of it.’

‘Funny place to find bones, under a wall,’ says Nelson.

‘They may have been a foundation sacrifice,’ says Max.

‘What’s that?’

‘The Celts, and the Romans sometimes, used to bury bodies under walls and doors as offerings to the Gods Janus and Terminus.’

‘Terminus?’

‘The God of boundaries.’

‘I pray to him whenever I go to Heathrow. And the other one?’

‘Janus, God of doors and openings.’

‘So they killed people and stuck their bodies under their houses? Funny sort of luck.’