Sherlock's bedroom door was always kept wide open at night.
It was a habit he had developed when Elizabeth was little. With his door open, he had an unobstructed view of the stairs, landing, and bathroom. He also happened to be a light sleeper, which helped immensely. He could hear if something was happening and could run and help without a stupid door being in his way.
One night Sherlock was awoken by the sound of someone coming down the stairs. He thought it sounded like John, but a glance at the shadow told him that it wasn't. Elizabeth crept across the landing and into the living room. Sherlock waited to see if she would go back upstairs, but after five minutes, he went after her.
She was sitting on the couch reading Jaber Crow by the light of the moon streaming through the windows. She didn't look up when Sherlock sat down next to her.
"Can't sleep?" Sherlock asked.
"No." Elizabeth said tersely.
"Any particular reason for it?" Sherlock pressed. His daughter's face was in shadow, so he couldn't deduce the information he wanted. It frustrated him when she puzzled him so. Even in the brightest light, she was sometimes hard to read. He liked to think that she got her mask from him.
"Not really." Elizabeth turned a page.
"Alright." Sherlock delved into his Mind Palace to pass the time. If Elizabeth went back to bed, he would do the same. But he also planned to stay down here with her if she didn't.
John raced down the stairs. He was going to be late!
He ran into the living room, frantically trying to find his mobile. When he finally located it among some animal bones, he straightened, preparing to dart out the door. But then a sight stopped him.
Sherlock and Elizabeth were both asleep on the couch. Sherlock sat against the cushions, and Elizabeth had her head on a pillow balanced on his lap. John took that opportunity to snap a photo of the family. Next time Sherlock claimed he felt no love, John could shut him up quick. Though granted, the detective had been using that line less and less frequently these days.
No matter what Sherlock said, everyone could see that he loved his daughter. Though John was never actually sure he had told her so.
But this was one of the moments that he showed her.