I said: ‘That’s it. You can forget the whole thing, Spoder. I’m not going to believe in a locked room mystery. It’s a hoax of some kind.’

‘I promise you this is serious. Look – I only downloaded the file last night. It is exactly as I found it.’

‘And I promise you that locked room mysteries are entirely a figment of the imagination of crime novelists. And even then, only from a small minority of crime novelists. Impossible crimes don’t happen in the real world – they can’t happen in the real world. Murder is brutal, irrational, usually impulsive. Murderers don’t hatch complicated schemes to baffle people who come along later. They are out to kill. They kill, then they try to get away. If it is planned at all, a murder is worked out in the vaguest way. To the typical murderer preparation and planning mean finding out when the victim routinely comes home from work. Or the licence plate number of the victim’s car. Or the lonely walk the victim takes every weekend. Other than that the motives are basic: money, sex, revenge, and so on.

‘Locked room mysteries are planned meticulously, often with almost mathematical precision. They are contrived, made up, invented, they have outrageous and insanely complicated explanations. Bullets shaped from frozen blood taken from the victim earlier under a pretence, clocks with microscopic poisoned darts that shoot the victim on the stroke of midnight, icicles that can be shot from hidden crossbows. That sort of thing. The locked room mystery depends on intense and detailed planning, logistics, exact timing of both the weapon and the behaviour of the victim. Everything has to happen precisely according to the plan. For that reason alone the entire subject is nonsense. The real world is too random and unpredictable. Things go wrong.’

Spoder listened to this in silence.

I went on: ‘If it’s recorded in the police file that Dever Antterland was murdered inside a locked room it means some hoaxer has accessed the file and made changes. Perhaps it was meant as a laugh. If the police actually found the room locked with Dever’s body inside, it can only mean the room was locked after the crime took place. Or it means they made a mistake and the room wasn’t locked at all. Or Dever’s body was found somewhere else and the file is wrong.’

‘I think the file is genuine,’ Spoder said, sounding crestfallen. ‘I recognize some of the names of officers who worked on this. In Raba as well as Sekonda. They weren’t the sort who made simple mistakes, or who would put false material on file.’

‘Well, I don’t want to be drawn into this. If you want to go over to Sekonda and see what happened then of course you’ll get your usual hourly rate.’

‘This locked room was different,’ Spoder said. ‘Really different.’