Author's Note: John and Mary might name their daughter Sarah Elizabeth and call her Beth (A veiled Doctor Who reference to Sarah Jane Smith, and John and Mary's choice of code word in "The Sign of Three").
Another late one. John Watson sighed contentedly into his cup as he took a long sip of the steaming, frothy liquid. He leaned against cabinets tiredly. The warmth and jolt of caffeine in his veins would keep him conscious for a little while longer. There was far too much to do to sleep now. Mary moved about the tiny kitchen of 221b domestically, no doubt cleaning up the partially eaten take-away from last night and making herself useful. John closed his eyes as his head started to throb painfully behind his eyes. A night of running on adrenaline had caught up with him. Suddenly, he remembered that his body was not as young as he believed it to be. Nevertheless, lack of sleep was worth the invaluable assistance he could provide to Sherlock Holmes. This time, he and Sherlock were tackling Moriarty together. Losing a few nights of sleep would be worth a thousand restful nights he could rest once Moriarty was truly where he belonged – dead.
From his comatose reprieve, he heard the voice of his daughter and allowed himself a weary smile. Her muttering echoed incoherently from the sitting room. Mary shut off the tap; then he could hear her better. He was surprised to catch a rich baritone intertwined with the lisping prattle that was music to his ears. "And dis one?"
"Vanessa atalanta." John opened his eyes and leaned forward to peek into the sitting room. There was the unlikely pair of them before the fireplace. His daughter stood on the arm of Sherlock's great chair. Normally, John would have reacted immediately to such action. Despite what Sherlock Holmes believed, furniture was not to be stood upon. Doing so could be quite dangerous. He restrained the impulse though. Sherlock stood protectively alongside her, one hand ready to catch her if she tottered and his other finger tips wrapped firmly in her hold. "Will it be a butterfly?" she asked Sherlock excitedly as she regarded the shadow box with wonder. John stifled a laugh. She did love butterflies.
"Yes. Of course not that one. It's dead." Tactful Sherlock. Always clarifying the logical. John watched as his daughter turned her face gravely to Sherlock. "Did you kill it, Sherwock?"
The detective paused briefly as he attempted to find the right words. "Yes," he finally said succinctly, suddenly appearing uncomfortable at her inquiry. John knew images of Magnussen must have been flickering through the man's mind – the man he had killed to keep the Watsons safe. He had killed to keep her safe.
His daughter pursed her lips as she contemplated the fate of the poor caterpillar. Then it was suddenly forgotten as she pointed hastily to another insect, wobbling on the armrest as she did. "Dis one. What it? Another butterfly?"
She thought it was the fate of all insects to eventually become beautiful butterflies. John smirked and noticed Mary watching him carefully. She motioned for silence as she grinned warmly while drying her hands on a dishtowel. She jerked her head towards the landing, and John sat down his cup. Hand-in-hand they retreated, leaving their daughter under the watchful care of Sherlock Holmes.
The thought seemed odd for a moment in John's brain. That night he had run across rooftops with Sherlock and chased a crazed cabbie across greater London to save the man's life, John would have never imaged having a wife and a daughter only a few years later – and having Sherlock Holmes so intimately connected with them. Brilliant, difficult, Bohemian Sherlock Holmes who delighted in the unconventional and kept body parts in the fridge on various occasions was never the man John thought of entrusting with the care of his daughter. Things had changed though. John's lips quirked upward in another tiny smile. Maybe Sherlock was right. Life was infinitely stranger than anything which the mind of man could invent. Maybe his Beth was right too. Maybe some things did turn out to be butterflies after all.