‘We’re talking about punctuation while this bloke’s trying to ruin my life?’

‘Humour me, Joe. How many times, do you think?’

‘No idea. Five? Six? A dozen?’

Naylor shook his head.

‘Just once. Just one single time: when he posted on Saturday to say he was OK.’

‘OK.’ I scanned the printouts on the desk, hoping to find something to prove the detective wrong. But there was nothing.

‘And how many times,’ Naylor continued, ‘do you think he used a full stop at the end of a status update in the last three months?’

‘None?’

‘Almost: just one.’

‘The post on Saturday?’

‘Yup. The linguistic analysis shows that he’s not a big fan of punctuation on social media. Never has been. Until this Saturday just gone, when he seems to have had something of a grammar revelation and he’s used a semi-colon, an apostrophe and two full stops in the same post. The five text messages we talked about just now – they also include discrepancies in the use of apostrophes, capital letters and the spelling of certain common words where he’s previously used textspeak abbreviations, but this time types them out in full.’

Larssen’s face was impassive, his unblinking eyes on the detectives.

‘And what preliminary conclusions have your university people drawn?’ he said calmly.

‘Their considered opinion is that Saturday’s Facebook post,’ Naylor tapped a thick index finger on the right-hand page, ‘is very unlikely to have been written by the same person who wrote these previous posts. Likewise these five text messages were very unlikely to have been written by the person who was previously sending texts from this number. In other words, not Ben Delaney.’

‘Well, that doesn’t make sense,’ I said.

‘How about you, Joe? You’re a history teacher, right?’

‘English.’

‘Bet you could teach Mr Delaney a thing or two about grammar and punctuation, couldn’t you?’

I said nothing, not wanting to dignify his tacit accusation with a response.

‘Spelling and full stops, apostrophes and semi-colons,’ Naylor said. ‘You must know all the rules back to front and inside out.’

‘Ben could have written them that way deliberately, to throw you off the scent.’

It didn’t sound convincing, even to me.

Naylor said: ‘Some sort of criminal mastermind, is he?’

‘He’s a very, very clever guy. I wouldn’t underestimate him.’

‘Proof of life, Joe. That’s what we’re about right now. That’s the name of the game. And I’ll be honest with you: this latest stuff is giving me real cause for concern.’

‘What about the message that appeared on my computer at home yesterday? He blames me for everything.’

‘No one saw that apart from you. Ditto your “close encounter” with Mr Delaney at the country park yesterday morning. You’re the only witness. How’s your hand, by the way? Your knuckles all right?’