Two of the residents of 221b Baker Street were sick with a stomach virus that had been going around. First, John had picked it up from his job at the clinic, then, because telling Rosie that her father was sick and she couldn't go near him for a little while, didn't go over well, the five-year-old had gotten sick, leaving Sherlock to play nurse for the both of them.
Mrs. Hudson was amused to see Sherlock spraying disinfectant over every surface of their flat while wearing a surgical mask the day after John and Rosie had caught the virus.
"Oh, dear, who's sick?"
"Both of them." Sherlock said shortly, spraying John's armchair liberally. "Everything's gone to hell."
"Well, I just came up to tell you that I'm going to visit my sister for a bit, but I might cancel my visit if you need help..." Mrs. Hudson said, looking a little guilty.
"No, no, leave. It's a twenty-four hour virus, I am perfectly capable of taking care of it myself." Sherlock said, stubbornly refusing to ask for help.
"Oh, well, if you're sure." And Mrs. Hudson gave him a smile and left the room.
Sherlock had thought getting the landlady to leave would have been more difficult, considering how maternal she was.
Sherlock heard footsteps on the stairs. He turned around to see John walking slowly down the steps, pale and weak.
"What are you doing out of bed?"
John looked up at him, "Rosie's hungry. I was going to make her something light so she could keep it down."
"What's that saying about how abominable doctors are as patients?" Sherlock muttered before stopping John with a hand to his chest. "Go back to bed. I'll make her some toast." He told John.
John looked absurdly grateful, "Really? You're okay with being caregiver?"
"Yes, of course, John, I'm perfectly willing to take care of the two most important people in my life. Go to bed, you look like you're about to keel over."
John smiled at him and made his way back up the stairs.
Sherlock brought the toast up to what he had termed the "quarantined room" a couple minutes later.
John was reading to Rosie in an effort to keep her entertained, because keeping a little girl in bed while she recovered from an illness required the same amount of effort as keeping a bored Sherlock from shooting the wall.
Both father and daughter looked pale and tired. The two of them had been vomiting and miserable since yesterday.
"Toast." Sherlock announced as he walked into the room, still wearing the surgical mask because he couldn't afford to get sick.
John gave him another tired smile and Rosie pushed herself into a sitting position.
"With jam?" The little girl inquired, her blond hair loose about her shoulders.
"No, just butter. If you manage to eat this without vomiting I'll make you another piece with jam."
Rosie looked quite pitifully disappointed. "Okay. Strawberry?"
"Yes, Rosie. Strawberry." Sherlock said, placing the two plates of toast in front of John and Rosie.
"What do you say to Dr. Sherlock?" John asked his daughter, taking a bite of the toast.
"Thank-you, Sherlock." Rosie said, smiling sweetly at Sherlock.
"At your service." Sherlock said, turning to leave.