‘My dear lady,’ Major Sweet began in tones more consistent with ‘My good woman’—‘My dear lady, there’s no occasion for hysteria. Yes—well, of course, if you insist. Be glad to. No doubt,’ said the Major hopefully, ‘we’ll meet your nephew on our way.’

Clinging to him, she appealed to Grant and Alleyn. ‘I know you think me too hopeless and silly,’ she said. ‘Don’t you?’

‘Not at all,’ Alleyn said politely and Grant muttered something that might have been ‘claustrophobia’.

Mr Mailer said to the Major: ‘There’s a continuation of this stairway that goes up into the basilica. If you’ll take Lady Braceley that way I’ll go back and find Mr Dorne and send him to her.’

Lady Braceley said, ‘It’s maddening of him. Honestly!’

Sophy said, ‘Would you like me to come with you, Lady Braceley?’

‘Oh no,’ she said. ‘No. Thank you. Too kind but—’ her voice trailed away. She still gazed at Alleyn and Grant. She wants an entourage, Sophy thought.

‘Well,’ Major Sweet said crossly. ‘Shall we go?’

He piloted her towards the upper flight of the spiral stairway. ‘I’ll come back,’ he shouted, ‘as soon as that young fellow presents himself. Hope he’s quick about it.’

‘You’ll carry on, won’t you?’ Mr Mailer said to Grant.

‘Very well.’

Grant, Alleyn and Sophy embarked on the downward flight. They could hear Lady Braceley’s heels receding up the iron treads together with the duller clank of Major Sweet’s studded brogues. Behind them the Van der Veghels shouted excitedly to each other.

‘It is only,’ roared the Baroness, ‘that I do not wish to miss a word, my darlink, that he may let fall upon us.’

‘Then on! Go and I will join you. One more picture of the Mercury. Joost one!’ cried the Baron.

She assented and immediately fell some distance down the iron stairs. A cry of dismay rose from her husband.

‘Mathilde! You are fallen.’

‘That is so.’

‘You are hurt.’

‘Not. I am uninjured. What a joke.’

‘On, then.’

‘So.’

The descending spiral made some two or three turns. The sound of running water grew louder. They arrived at a short passage. Grant led them along it into a sort of ante-room.

‘This is the insula,’ he said. ‘You might call it a group of flats. It was built for a Roman family or families somewhere about the middle of the first century. They were not, of course, Christians. You will see in a moment how they worshipped their god. Come into the Triclinium. Which is also the Mithraeum.’

He motioned them into a cave-like chamber. The roof was vaulted and studded with small stones. Massive stone benches ran along the sides and in the centre was an altar.

Grant said, ‘You know about the Mithraic cult. There’s no need for me—

‘Please! But please,’ implored the Baroness. ‘We would like so much! Everythink! Please!’