His phone was ringing- that was probably what had woken him. John was out, getting milk or dating or something- did it matter?- but he usually texted. He didn't look at the screen as he picked up his phone, swiping his finger across the screen and tucking it between his ear and shoulder. "What?"

"Sherlock. I- well. I need you to come to the address I'm going to send you." Mycroft sounded far more tired than Sherlock could remember hearing in a long time. "I'm dying."

. . .

It was stupid. So goddamn stupid. One little chink in security which proved to be just enough. Because Mycroft couldn't let sleeping dogs lie and had to manhandle the damn thing, had to put the paperweight in his breast pocket and carry it around. And now here he was, strapped to God only knew how many machines, dying.

Mycroft knew he was dying- it was obvious. Opiate drips lined his arms to hold back pain so strong it threatened to overwhelm him, and even then he could feel his body crumbling away. If he thought about it, he could almost hear his cell walls collapsing.

The walls, the ceiling, the goddamned floor were lined with lead and concrete to block gamma rays from poisoning others. The room was huge- twenty foot walls, gray and boring, forming a cage of lead and concrete, designed to keep radiation in and people out. The only thing to break the stark evenness was a screen that took up half the far wall and the camera above it, the only remaining link to his brother and the outside world.

"There has to be a cure! Radiation has been around forever, there's treatments, I know there are. I've studied them!" He was bellowing, pacing and tearing at his hair. Mycroft couldn't die. He couldn't. Not like this. Anyone could get radiation, from being around x-ray machines or having cancer treatment or any other number of reasons. "Why aren't there protocols in place to prevent this?" he screamed, waving his arms at the television screen on the wall before him.

Mycroft was pale and green at the same time, hair already patchy and skin sagging from his bones. There were growths - keloids - emerging from his skin, and Sherlock found it hard to call to mind the brother he remembered, the brother who hid his strength in well-tailored suits - the brother who now weakened by the minute in beige scrubs, hardly able to breathe. "Fuck you!" The words emerged before Sherlock could even think them, directed into the face of a well-meaning nurse who had come over to speak with him. "Can't you cure him? All this science we have and you can't even cure one person."

He drew in a breath, tears welling in his eyes, and turned away. Three hours. That was the maximum amount before Mycroft- the detective swiped at the tears angrily, burying the hurt beneath fury and the knowledge of his brother's own ticking clock beneath all of that.

"And you!" Sherlock rounded on the television, glaring fiercely at the dying man. "You sodding idiot. Who the hell carries around a paperweight made of scrap metal with them?" Even though it would have done the damage anyways. Within the five meter radius- "In your pocket? You put a fucking paperweight in your pocket?"

Mycroft rasped on the screen, struggling for breath, and jabbed at the button that released a pain killer so strong it was on level with the cocaine Sherlock so favored in his youth. Except there was no limit on the drug dispenser for Mycroft. No doctor would ever touch him again.

"You are not going to die," the detective growled, advancing on the screen. "You are not allowed to die and leave me with this- this-" He waved his arms about him then fell silent, pressing his left forearm to his mouth and nose to hold back a sob.

"YOU ARE NOT ALLOWED TO FUCKING DIE, MYCROFT!" His throat was raw after the first word, and on the fourth he brought both fists down on the screen, again and again till shards riddled the skin of his hands and cracks marred the image of his brother, who was trying to stand, trying to walk towards the screen - not that it mattered, Sherlock doubted they were even on the same floor.

But now the tears were coming fast, and his collar was wet and his hands hurt and Mycroft was still dying and there was nothing he could do. He regretted wrecking the screen, because now Mycroft had fractured into one hundred smaller pieces, shards of leg and IV drip and bald patches distorted in the center. The detective crumpled to the floor in a heap.

"Go back to bed, My," he murmured, just loud enough for the microphones to pick it up. "You won't be able to stand much longer." But the man kept coming, and then sat painfully, stiffly against the screen on the wall, clutching his IV. He hacked wetly into his arm, chest rattling with diseased phlegm, and turned to look at the image of his brother, who for all his health was more broken than him.

"Sherlock.." And say what? his mind whispered. "You'll be alright." It felt inadequate, and it was, such a pathetic thing to say when one was dying. There was no guideline for this, no set rules of engagement for how to comfort loved ones when they grieved for you.

He coughed again, coughs that felt like they were tearing his chest apart. They probably were - there was blood smattering his sleeve now, and he wished he'd brought a blanket from the bed - he was so cold, but it was so far away. He heard a snuffling sound and turned to a sight he'd thought would never be seen again - his brother was crying, sniffling and choking on snot, arms curled around his knees where he sat on the floor. "I'm gonna miss you, My," he whispered, voice hoarse and eyes red. "Please don't die."

.

It was several minutes before Sherlock demanded to be let in to see him, radiation be damned please he's my brother I need to see him PLEASE, and the nurse was forced to sedate him. It wasn't much, just a bit of general anaesthetic, but when he came to the wrecked screen before him was dark and silent. No. No.

But he was gone. When a nurse came to check on him, he learned that Mycroft had died a half hour ago (too late to say goodbye) and that the room was being sterilised. There would be nothing to bury, no ashes to scatter - it was too dangerous to recover the body.

Sherlock didn't know how much time passed before John was there, hugging him as he stared at the screen, then requesting a first aid kit to clean his hands, then talking about going home. It was only when he began to try to help Sherlock to his feet that the detective lashed out, knocking John's hand away. He couldn't hear a word John was saying, he just knew that his brother was somewhere, gone, gone, gone, and there was nothing to be done, no crime to solve. So he sat and stared at the screen, mind quiet, too quiet, unable to process the loss of his brother.

Gone.

A/N: Title taken from this poem by Dylan Thomas:

Do not go gentle into that good night,
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.

Though wise men at their end know dark is right,
Because their words had forked no lightning they
Do not go gentle into that good night.

Good men, the last wave by, crying how bright
Their frail deeds might have danced in a green bay,
Rage, rage against the dying of the light.

Wild men who caught and sang the sun in flight,
And learn, too late, they grieved it on its way,
Do not go gentle into that good night.

Grave men, near death, who see with blinding sight
Blind eyes could blaze like meteors and be gay,
Rage, rage against the dying of the light.

And you, my father, there on the sad height,
Curse, bless, me now with your fierce tears, I pray.
Do not go gentle into that good night.
Rage, rage against the dying of the light.