‘Aha!’ I said. ‘So it might be the same person.’

‘Who can change their clothes in less than two seconds?’ asked Lesley. ‘Do me a favour.’

All the evidence files are linked, so I checked to see whether the Murder Team had managed to track WITNESS A as he left the crime scene. They hadn’t and, according to the action list, finding him had become a priority. I predicted a press conference and an appeal for witnesses. Police are particularly interested in talking to... would be the relevant phrase there.

Smurf Hat had been tracked all the way down New Row, exactly the route Nicholas had said he’d taken, but vanished off the surveillance grid in St Martin’s Lane. According to the ‘action’ list, half the Murder Team were currently scouring the surrounding streets for potential witnesses and clues.

‘No,’ said Lesley, reading my mind.

‘Nicholas …’

‘Nicholas the ghost,’ said Lesley.

‘Nicholas the corporeally challenged,’ I said, ‘was right about the murderer’s approach, the method of attack and cause of death. He was also right about the getaway route, and we don’t have a timeline where WITNESS A is visible at the same time as Smurf Hat.’

‘Smurf Hat?’

‘The murder suspect,’ I said. ‘I need to take this to the Murder Team.’

‘What are you going to say to the SIO?’ asked Lesley. ‘I met a ghost and he said that WITNESS A put on a mask and did it?’

‘No, I’m going to say that I was approached by a potential witness who, despite leaving the scene before I could get his name and address, generated potentially interesting leads that may further the successful outcome of the investigation.’

It made Lesley pause at least. ‘And you think that’ll get you out of the Case Progression Unit?’

‘It’s got to be worth a try,’ I said.

‘It’s not enough,’ said Lesley. ‘One: they’re already generating leads over WITNESS A, including the possibility that he was wearing a mask. Two: you could have got all that information from the video.’