‘We still have a problem, Cashbone. We need to work together – but you need to stop pursuing the girl, you understand?’

Cashbone was unyielding. ‘Not that simple, buddy. I need her. The COI needs her. Sunny Somerfeld died to bring this project to fruition and I’m going to see it through. We owe Sunny that.’

This was outrageous, to use Sunny’s name in such a manner. Wilde couldn’t stomach Cashbone a moment longer.

‘I’m going now, on foot – if you want to try to follow me, feel free.’

Wilde strode out of the broad-fronted hospital and turned right down Trumpington Street. He didn’t bother to look around to see whether Cashbone was pursuing him. Nor did he see the elderly woman with the blue rinse climb into the passenger seat of an Austin 10, which then did a U-turn and began to grind its way down the road at a discreet distance behind him. In the race here from Girton, he hadn’t seen the little car trailing in their wake.

After a few hundred yards, Wilde ducked into the ancient gateway of his college and sought out the head porter, Scobie.

‘Keep a weather eye out for strangers today, Scobie. If you don’t know someone, don’t give them admittance. OK?’

‘Of course, sir – and welcome back from wherever you’ve been.’

‘If anyone asks for me, tell them I’m uncontactable.’

‘I understand, sir.’

‘The only calls I will accept are from Miss Morris, Dr Weir or Mr Eaton.’

‘I shall make a note of it, professor.’

For a brief moment, Wilde wondered whether he could be endangering the porters. But he had confidence in them; they might look like ledger clerks in their bowlers and office suits, but these men were solid in defence of their colleges and all those in them. Anyway, the chance of Charles Young trying to force his way into a Cambridge college was vanishingly small.

Wilde crossed the courts and ascended the staircase to his room. Bobby, his college servant, greeted him, but Wilde wasn’t in the mood and merely grunted back.

‘Coffee, professor?’

‘No, I’ll be no more than two minutes. I want you to go out into the new court and keep an eye on the gateway. See if anyone is loitering, then come back and report to me.’

‘Certainly, sir.’

His rooms were cold and unlived-in. Everything was where it should be, but there was ice inside the windows and his books and papers all looked like things from another life. Two minutes later, Bobby returned.

‘All clear, professor. No one about except Mr Scobie.’

‘Right, now we’re going back. You’ll be twenty or thirty yards ahead of me. If you carry on walking, it means there’s no one about. If you stop, it means you’ve seen a stranger – someone not associated with the college. Is that clear?’

‘Yes, sir.’