Sherlock called me just before 5am. Somehow he had become aware of a body found on the tracks outside London Bridge. The police were as thrilled to see us as I was to be awake that early. It was worth the early start, though, as when we got there we found a man with no ticket, no phone, and no signs of a struggle. The police wanted to file it as a routine suicide, but Sherlock could tell something was off and managed to look at the body while I distracted the officers. He was right.

Sewn into the lining of the man’s coat - genuinely sewn, someone had done this with a needle and thread — were printed schematics for a surveillance drone. We visited the company’s office in Greenwich and they confirmed the set was incomplete. Junior engineers with spotless records don’t wander onto live rails at 5am carrying classified intel. Holmes had the how the same morning: he’d travelled along the tracks, not beside them. On the roof of the 04:51.

The missing sheet took us to the Shard. I’d always taken the building at face value — an impressive piece of architecture with very little inside. Holmes got hold of the architect’s floor plans and decided to start counting. Unfortunately this involved taking every flight of stairs. Despite running out of breath and my legs feeling ready to fall off, I noticed the same thing Sherlock did: the numbers didn’t add up. Above the viewing gallery were floors that didn’t exist on paper, served by a lift with no buttons — it only went to one place.

What we actually found up there, I’m not actually allowed to write down, and I am aware the Home Office keeps track of this website and its content. The short version: a private military outfit with a headquarters - and I must be clear here - the UK Government has no association with or knowledge of. They had a keen interest in where its drone designs had wandered off to. The engineer had worked out what his employer was really building, and who it was for. Where he was taking the plans we don’t know, so whether his death was in vein or tragic step towards the right destination is something I still think about.

The arrests happened quietly, and the sentencing even more quietly if you catch my meaning. We haven’t been back inside The Shard since, but my leg muscles seem to seize up slightly anytime I pass through Southwark.