John thinks, if he could freeze a particular moment like a photograph, there are several he could choose from.
The heat, rising from the Afghan midday to his brain; the first, dazzling, blast of sunlight from alien territory as he stepped out of the aircraft. Nerves enough to make him feel sick – but sheer excitement, anticipation of the unknown, a heart-swelling, lump in the throat feeling of making a difference. Being flanked either side by other men all fiercely willing to fight for a cause, even a cause so muddled with political stirring that it no longer seemed clear, the sense of belonging. Yes, John would once have chosen that moment. But now, looking back with the twinge of his scar and the memory of too many faces which didn't come home, he thinks not.
Maybe the moment he saw Harry walk towards Clara, pride and love bursting from his face as she made her vows, white dress defiantly traditional and his parents, his parents smiling at her too. He had felt a sense of complete peace and rightness at seeing his beloved little sister so happy, so free as she entered into her lifelong contract to love someone else. Yet, once again hindsight smudges the ink of this snapshot, Harry's discarded phone a symbol of a photograph that depicts a false memory.
So he chooses this moment. Darkness and heat. Only a silhouette and stunning clarity, the soft murmur of Sherlock's breathing, the nerve endings in his skin firing tiny sparks at every touch of that dark hair, a sense that the sheer intricacy of this exact second is pressing upon his every inch of skin and making his breathing slower – but above all, simplicity. Two faces, under cover of night, pressed nose-to-nose, sharing the secret of intimacy without breathing a word, and the knowledge that they will still be there in the morning.