He was succinct and adequate, Sophy grudgingly admitted. The basilica of San Tommaso, he said, was one of a group of monuments in Rome where the visitors could walk downwards through the centuries into Mithraic time. At the top level, here where they now stood, was the twelfth-century basilica which in a moment they would enter. Beneath it, was the excavated third-century church which it had replaced. ‘And below that—imagine it—’ said Mr Mailer, ‘there has lain sleeping for over eighteen hundred years a house of the Flavian period: a classic “gentleman’s residence” with its own private chapel dedicated to the god Mithras.’ He paused and Sophy, though she regarded him with the most profound distaste, thought: He’s interested in what he’s talking about. He knows his stuff. He’s enjoying himself.

Mr Mailer went on to describe briefly the enormous task of nineteenth-century excavation that had so gradually disclosed first, the earlier basilica and then, deep down beneath it, the pagan household. ‘Rome has risen, hereabout, sixty feet since those times,’ he ended. ‘Does that surprise you? It does me, every time I think of it.’

‘It doesn’t me,’ Major Sweet announced. ‘Nothing surprises me. Except human gullibility,’ he added darkly. ‘However!’

Mr Mailer shot him an uneasy glance. Sophy gave a little snort of suppressed amusement and caught Barnaby Grant looking at her with something like appreciation. Lady Braceley, paying no attention to what was said, let her ravaged eyes turn from one man’s face to another. The Van der Veghels, standing close together, listened intently. Kenneth Dorne, Sophy noticed, was restless and anxious-looking. He shuffled his feet and dabbed at his face with his handkerchief. And the tall man, what was his name—Allen?—stood a little apart, politely attentive and, Sophy thought, extremely observant.

‘But now,’ Mr Mailer said, ‘shall we begin our journey into the past?’

The woman with the postcards had sidled between the group and the entrance. She had kept her face down and it was still shadowed by her black headscarf. She muttered, almost inaudibly, ‘Cartoline? Posta-carda?’ edging towards Sebastian Mailer. He said generally to his company, ‘There are better inside. Pay no attention,’ and moved forward to pass the woman.

With extraordinary swiftness she pushed back her headscarf, thrust her face up at him and whispered: ‘Brutto! Farabutto! Traditore!’ and added what seemed to be a stream of abuse. Her eyes burned. Her lips were retracted in a grin and then pursed together. She’s going to spit in his face, thought Sophy in alarm and so she was, but Mr Mailer was too smart for her. He dodged and she spat after him and stood her ground with the air of a grand-opera virago. She even gave a hoarse screech of eldritch laughter. Mr Mailer entered the basilica. His discomforted flock divided round the postcard-seller and slunk after him.

‘Kenneth, darling,’ Lady Braceley muttered. ‘Honestly! Not one’s idea of a gay little trip!’