When Victor Trevor had asked him to accompany them to the London School of Hygiene and Tropical Medicine, John Watson had assumed he was required for his medical knowledge and that they would be visiting that day. He was mostly correct: Sherlock thought John’s knowledge could prove useful, or at least save them some time, and although they were going that day, it was not until eleven o’clock at night that they left Baker Street.

Sherlock had wanted to take a taxi, but Victor had insisted they walk, so they’d made their way down New Cavendish Street until they reached their destination. John carefully looked the other way when they opened the door, and hoped this was an operation sanctioned by Mycroft, and that no suspicious person would confront them.

Now it was midnight and he was standing in a laboratory looking at the labelled trays of test tubes by the light of Victor’s torch. He pointed out a couple of possibilities and Sherlock prised the trays out. The first tray looked intact, and he sensed Sherlock and Victor’s frustration, but the second tray had gaps in it.

“We need to know which ones are missing,” Victor muttered. “John, can you turn them so we can see the labels, but be quick, it’s all taking too long.”

Hurriedly, John turned the test tubes and Victor took several photos, while Sherlock held the torch. Sherlock then pushed the tray back into its place and Victor said, “Come on, we need to leave NOW! Sherlock, there’s no time.”

The three of them walked as quickly as they could down the dark corridors, Victor leading. Then, as he slammed the outside door shut, the alarms began.

“This way,” Sherlock called.

They followed him into the smaller side streets, where he led them in a zigzag way, back to the main road.

“Do we walk back?” John asked.

“No,” Victor replied. “We’re more likely to be noticed now. We’ll take the night bus, just three mates who’ve had a bit too much to drink and are heading home. We’ll have to go a couple of stops past ours and walk back from there, but that won’t take long.”

They did as he suggested, and once back at Baker Street, John put the kettle on, while Victor sent his photos over to Mycroft. By the time the tea was made, Victor was grinning at his phone.

"What’s so funny?” John asked.

“Mycroft’s vocabulary is expanding. He never used to know as many swear words as he’s just used.”