It took Sherlock three hours to completely retrace their steps from the past several days, and another two to convince Inspector Lestrade to help him regain access to the case from six days before.
In six minutes, he had narrowed down the one place that John had been that no one else had.
He had a water sample from the basement apartment master bedroom's air conditioner in under a minute.
Including the half hour it took him to return home in a cab, it took him 2 minutes to theorize and confirm his diagnosis.
Within another twenty minutes, he was being yanked backwards by security in Saint Bart's hospital as he shouted at the top of his lungs, "It's Legionellosis!"
He was thrown out of the hospital for twenty minutes, until Dr Mike Stanford came to fetch him from outside, saying simply, "You're right, of course. Legionnaire's disease. We've got him on levofloxacin now. You'll be even happier to know, last time John was conscious he kicked Harry out and signed a form to make you his medical proxy."
"Spare me the details, get me inside."
As he listened to the steady noise of the heart monitor, Sherlock Holmes, genius consulting detective, pondered how strange it was that something as essential to life as water could also be so very deadly. Never had he thought it would be this bad. He smoothed another crease out of the blanket beneath his long fingers and fiddled with a stray thread trying to escape from the sleeve of the pale blue hospital gown wrapped around John's thinning frame. The cogs of his mind whirled as he replayed the last two weeks, trying to figure out what he had missed, where he had faltered, what he could have done to prevent...but it was no use. There was only chance to blame; chance and that stupid spa.
"Molly told me a joke today." His voice was much softer than normal, barely more than a soft whisper. "Two scientists walk into a bar, and one orders a glass of H2O. His companion then says, 'I'd like a glass of H2O too'. When both their drinks arrive, the first man finishes his glass in one long draught, and the second dies just after his first swallow. Can you guess why?" Only the cyclic 'bwoop bweep' of the machine answered him.
A smooth voice behind him made him cringe, "Because H2O2 is a deadly poison when consumed."
"Go away, Mycroft!" The detective spat out in clipped tones.
Instead of his brother's voice, the only sound he could hear above the beeping was his brother's expensive shoes and umbrella tapping along the hospital linoleum. His elder brother was silent for a long moment before asking, in an oddly kind tone, "How is he?"
"Yes, Sherlock, even that pathetic pathologist you despise could have observed that." Mycroft was he only person Sherlock had ever known besides Mummy who could make exasperation sound almost elegant. "I was asking for a more in depth analysis in regards to whether or not our dear friend shall recover."
The chair the detective had been occupying clattered to the floor as he rose abruptly, trying his best to loom menacingly over his brother. "My friend shall recover in due time, no thanks to you!"
"Sherlock, the mortality rate..."
"Do not speak to me about disease mortality rates!" Sherlock hissed venomously. "Get out, Mycroft! Get out of this room before I commit fratricide!"
For a long moment, while Sherlock shook with impotent rage, Mycroft simply stared into his younger brother's pale eyes and his face softened. Their gazes stayed locked for a full two minutes before Sherlock slumped weakly onto the edge of the hospital bed and pushed his face into his hands. As his younger sibling took a moment to recompose himself, Mycroft awkwardly set the toppled chair back onto it's legs and twirled his umbrella against the floor.
Even more awkwardly, he helped his brother back into the chair, and searched out one of his own. They sat in silence for another half an hour, with Sherlock staring at the spike and valley of the EKG and Mycroft gazing without focus at the rain-spattered window on the other side of the room. Taking a deep breath, Sherlock brought his fingers to his lips as if in prayer, and Mycroft glanced side-long at him.
"I think," the detective said, in a quiet, considering way, "I may be afraid."
Mycroft held his breath quietly, afraid to so much as blink. His brother had not confided in him (without an intervention) since they were small children.
Sherlock gripped the arms of his chair, his eyes lowering to some spot on the floor. It was some time before he spoke again, in a slightly strained, small voice, "He's my only friend, My."
Slowly, Mycroft brought a hand to his little brother's shoulder, squeezed it lightly, and left it there. The fact that Sherlock did not shrug him off spoke even more volumes than the slight tremor shaking the detective's frame. Focusing his gaze on the still body of John Watson lying prone in the hospital bed before them, Mycroft answered just as quietly, "I know, 'Lock. I know."
When he arrived at the hospital that morning, he hoped to find his best friend at least awake. What he found was an empty room.
Turning to find Mike Stamford behind him, Sherlock lurched forward and grabbed the small man by the shoulders. "Mike," he growled, but the doctor cut him off.
"Don't get your knickers in a twist, Sherlock. He's been moved to a private room, courtesy of your brother." Smiling jovially, the plump doctor clapped the detective on the elbows. "And he's awake."
Sherlock's smile was brilliant for the half a second it was visible before he disappeared down the hallway.
He got turned around four times before he lowered himself to ask a nurse for John's room number.