Sara looked over to Patrick. ‘Rayah will be able to confirm the timings, she was in the office when I got back.’

‘You mean Ms Yaseen,’ said Buttler.

‘Yes.’

‘Ms Yaseen,’ said Buttler smoothly, Sara smelling another unwelcome surprise, ‘has stated that you returned to the office around 6.30 p.m. and then left sometime around 7.15, 7.20 p.m., shortly before she herself departed for the evening.’

‘Then at least you have that,’ said Sara frostily.

‘She was, however, unable to confirm that you had actually left the building.’

‘What else would I have been doing?’

‘Ms Shah, I am only laying out what we know for sure and what we don’t.’

‘How do you know Rayah herself left?’ said Sara.

‘Fair point.’ Buttler made a show of an agreeable concession. ‘And we will be checking her phone records too and her friends’ confirmation of her arrival time.’ He smiled, as if none of the three of them should be in the slightest bit worried at the direction his train of thought was taking. ‘There is one final curiosity,’ he resumed. ‘Miss Shah, did you notice any particular smell when you discovered the body.’

That whiff of paraffin hit her like a dart. She wasn’t prepared for the question or where it could lead. ‘I’d just stumbled across the dead, half-naked body of a man I had been having a professional conversation with some four hours earlier. I hope you’ll forgive me if my senses were numbed.’

‘I quite understand. Perhaps you could answer my question.’

‘Mr Buttler,’ interrupted Patrick, ‘you’re going over a certain mark of which you’re well aware and I must ask you again either to desist or move to a formal procedure.’

Buttler turned to him, all twinkles and humour banished. ‘No more questions after this, Mr Duke. I assure you again it’s in all our interests to get to the end of this.’

‘It’s OK, Patrick,’ said Sara. ‘Whatever track he’s on, it’s wrong.’

‘Thank you, Ms Shah. So?’

‘I’m sure there were smells of different sorts but I was too shocked by what I was seeing to notice any.’

‘The reason I ask is that clear evidence has been found of a medical cleanser, perhaps some form of paraffin-based wipes, on the bared skin of the naked man, mainly around his private parts, pubic hair and lower belly.’ Sara began to see the trap – and how neatly it must have been laid. ‘The obvious explanation is that another person was with Sir Francis and cleaned that skin in order to avoid the possibility of any residual DNA evidence of their presence.’ Buttler paused; Sara and Patrick watched him silently. ‘The implication is that the other person or persons present feared residues of their body fluids may have been present and wished to eliminate them.’

‘Unless Morahan cleaned himself before expiring,’ said Patrick.