We started with caution plus two, which involves us scaring the interviewee to death with the normal caution – ‘You do not have to say anything, etcetera, etcetera . . .’ – and then right when they’re sure we’re going to march them off to the cells we throw in ‘but you are not under arrest at this time and are free to leave if you want to’ at the end. The solicitor nodded sagely as Guleed reeled it off, Olivia stared at the table and Lady Ty gave me a sour smile at ‘free to leave’.

Guleed warmed up by asking where Olivia went to school. St Paul’s, which was a hideously expensive private school in Hammersmith, although because she was a day student it probably only cost the equivalent of a police constable’s starting salary. She was hoping to go to Cambridge, but first there was the gap year – Olivia pronounced it ‘gap yar’ – when she planned to do good somewhere in the third world.

‘Teaching English,’ she said. ‘Or building orphanages – I haven’t decided which.’

‘Somalia perhaps,’ said Lady Ty. And then, to me, ‘or Sierra Leone.’

‘Mrs Thames,’ said Guleed, ‘I’d be grateful if you could allow your daughter to answer the questions on her own.’

I saw a flash of anger on Lady Ty’s face followed by a hint of amusement and respect.

Guleed asked where Olivia lived, whether this was her only address and other questions she already knew the answers to but which allowed her to circle around to where Olivia had been last night. I clocked the brief – he looked a bit complacent to me, but there was a sheen of sweat on his lip. Family solicitor, I decided, more used to conveyancing and moving Lady Ty’s wealth around than to police interviews.

‘Was your mum here last night?’ asked Guleed.

Olivia hesitated and her eyes flicked towards her mum, who stared fixedly at Guleed.

‘Yes,’ said Olivia, ‘as far as I know.’

‘Was your father at home too?’ asked Guleed.

‘He’s out of the country,’ said Lady Ty.

Guleed asked where he might be.

‘Is this relevant?’ asked the lawyer.

‘Just establishing a timeline,’ said Guleed.

‘He’s in Dubai,’ said Lady Ty. ‘On a contract.’

‘Really,’ said Guleed. ‘What kind of contract?’

‘He’s a civil engineer,’ said Lady Ty and then, staring directly at me, said, ‘He specialises in hydrology, water management systems, that sort of thing.’ She looked back to Guleed. ‘He’s the top man in his field.’