The Tontine (джен)

Sherlock and John take on a new case that brings John's military history and secrets to the table. The detective is forced to understand that there is a great deal more to John than jumpers, tea, and a love of adrenaline. (Takes place after the Reichenbach Fall, no Mary. There is no smut in this part of the trilogy and it can easily stand alone.)
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Sherlock looked to John, eyebrows furrowed, "You have higher security clearance than my brother?"
John licked his lips, eyes flicking from one Holmes brother to the other, both staring at him with equal ferocity and confusion, "Well," he said, "Technically, due to the nature of... yes."