When Mycroft Holmes arrived at Baker Street with his briefcase full of papers, then trouble was usually not far behind. Fortunately, Sherlock Holmes was not adverse to a little trouble, and John Watson generally needed little persuasion.

'Did you know him?' Mycroft asked.

'Yes,' John said, looking at the photograph of an army officer in front of him. 'I served with him in Iraq. What happened?'

'That,' Mycroft said, 'is exactly the question. The official line is that Major James Richardson was shot by an interpreter who was working for the Taliban as a random act of insurgency. What the Royal Army Medical Core are not aware of is that he was also working for the British Government .

'He was an undercover agent? 'John Watson asked. 'Since when?'

'Since shortly after you were posted with him in Iraq. So will you take the case?'

'Too busy,' Sherlock said, as John said, 'Yes'.

John looked at Sherlock. 'Please.' he said, then when Sherlock failed to respond, 'He was a friend. We worked together, we watched each others backs. I owe him this much.'

Sherlock shrugged. 'Very well,' he said, and reached out a hand for the file. In reality he was bored and any case was a welcome diversion, but obliging Mycroft without complaint or resistance was against all of his principles. 'Is it all in here?'

'Of course, together with contact details for witnesses and relatives.'

'The interpreter who shot him?'

'Was shot by one of the soldiers on guard duty.'

'Any other casualties?'

'No'

'What happened?' John Watson asked. 'I'm presuming that it wasn't a random attack by a stranger?'

'They were awaiting an influx of casualties at a Casualty Clearing Station after a bombing in a market place. Major Richardson was talking to the interpreter, we presume obtaining phrases in local dialect when the interpreter pulled a gun and he was shot at point blank range. The interpreter was then taken down by one of the officers providing defence.'

'First mistake,' Sherlock Holmes said, then to Mycroft's raised eyebrow. 'John, tell him.'

'He wouldn't have needed to talk to the interpreter,' John said, 'Not for any period of time. Mass casualty situations like that are like veterinary medicine. You go through triaging people into dead, unsalvageable, need immediate treatment and 'walking wounded can wait'. In situations like that the only things that you need to be able to say in the local dialogue are, 'Point to where it hurts' and, 'Shut up.' There's no time for anything else. He wouldn't have spent time talking to the interpreter to get more dialect, he would have been checking kit, drawing up drugs, not learning how to say, 'What medication do you normally take?' in the local dialect because he wouldn't have cared.

'So he was asking the interpreter something else, or the interpreter was telling him something else,' Sherlock said. 'This is becoming more interesting. Full military clearance, Mycroft?'

'Of course.'

'And the regiment he was stationed with are where now?'

'Aldershot.'

'How about the medical team that he was working with?'

'Frimley Park Hospital I believe, not a great distance away, or working on the base at Aldershot.'

'We'll get onto it.'

'Don't pretend that you're not interested in this case,' John Watson said to Sherlock shortly after the door had closed behind Mycroft. MI6 officer, shot in Afghanistan by an alleged insurgent who wasn't what he seemed, this has got our names all over it, surely?'

'Maybe, maybe not.'

Three hours later and the table at 221b was covered in documents and photographs of the shooting. The military records of Major James Richardson, and what records were available for the interpreter had been analysed in depth. The MI6 records for Major Richardson were more elusive initially, but even MI6 records were little challenge for Sherlock's less legal IT skills. Frustratingly they were incomplete, and not even Sherlock Holmes could find details of Major Richardson's last mission.

'It doesn't make any sense,' John said, 'MI6 had an undercover agent in Afghanistan, working side by side with Afghan army personnel, who we know often switched between sides, and they didn't have him working on anything? I don't believe it.'

'There's no evidence that he wasn't working on anything,' Sherlock said, 'there just isn't any evidence that he was. Yet again you're confusing lack of positive evidence with proof of the null hypothesis.'

'So he was working on something?'

'Of course, its the only logical explanation.'

'But what?'

'That, is the million dollar question. Lets go to Aldershot.'