The door slid open to reveal the next room. Sherlock didn't move. Instead he remained on the floor with his knees to chest and his head stooped. The television lay smashed on the ground beside him; buzzing faintly and flashing sporadically. His knuckles were aching from driving his fist through the screen; his chest tight, stomach turning.

"Sherlock." John's voice broke. He cleared his throat, stopping for a moment to compose himself. "Sherlock, you have to get up. We have to keep going."

Sherlock raised his head slowly, looking up at John with red, watering eyes.

"This is what she wanted," John continued. "She wanted to break you. You can't let her."

"I'm waiting…" Eurus sang over the speaker.

"John is right," said Mycroft. "We need to move on."

"Don't you dare," Sherlock hissed. He stood up and marched towards him, his movements fuelled by venom. "This is your fault."

"My fault?"

"You knew how dangerous our sister was. You knew what she was capable of and yet still, you handed her the opportunity to do all of this like a gift. You killed her. You killed my–"

John placed himself between the brothers. "Come on, we can't be doing this."

Mycroft straightened his back, collecting himself with a deep breath. "I… I'm sorry. I cannot begin to imagine how you f–"

"No, you can't. But I can," John interrupted. "Actually, I don't have to imagine."

Mycroft dropped his head.

John turned to Sherlock. "I know you're suffocating right now. I know the agony you're feeling is like no physical pain you've ever felt before. But Sherlock, there is a child waiting at home for his mum and dad…" He took a sharp breath, his eyes filling with tears. "His mum's not coming back. But his dad… His dad still can." He reached out his hand. "Today we're soldiers. For Vaughan. For Rosie. For Mary and Margaux. We have to keep going…"

III

The room was empty besides a television mounted on each cold, grey wall.

"Hey sis," said Sherlock as he walked around the room. His voice was stern and angry. "Don't mean to complain but this one's empty. What happened? Did you run out of ideas?"

Each screen came to life with the image of Eurus, still sitting behind the desk, still glaring down the lens.

"It's not empty, Sherlock. You've still got the gun, haven't you? I told you you'd need it, because only two can play the next game. Just two of you go on from here; your choice." She grinned. "It's make-your-mind-up time. Whose help do you need the most? John or Mycroft?"

Mycroft looked across to John with a frown as John winced in disbelief.

"It's an elimination round. You choose one and kill the other. You have to choose: family or friend. Mycroft, or John Watson?"

The lights in the room dropped to a deep, blood red. Jim Moriarty appeared on screen, clenching his teeth.

Tick-tick-tick-tick-tick-tick-tick–

"Eurus, enough!" Mycroft shouted.

The lights turned white as the picture of Eurus returned.

"Not yet, I think," she said. "But nearly. Remember, there's a plane in the sky, and it's not going to land."

Mycroft knew immediately who needed to live. And it wasn't him. He straightened his posture and stepped forward, adorning a snarl as he began to speak.

John stood proud as Mycroft hurled insults at him, keeping his mouth pressed firmly closed as he watched him demand Sherlock shoot him. He had been a soldier, and today, they were all soldiers. This was what he had to do.

Yet like Sherlock often did, he saw through his brother's façade. Beneath the cold, mean veneer stood a man who had always cared for him. A man who was willing to die for him. He lifted the gun and aimed it at Mycroft.

"Sherlock. Don't," John whispered.

Mycroft turned to him. "It's not your decision, Dr Watson." He looked back to his brother with a smile. "Not in the face, though, please. I've promised my brain to the Royal Society."

Sherlock closed his eyes for a moment. "where would you suggest?"

"Well… I suppose there is a heart somewhere inside me. I don't imagine it's much of a target but… why don't we try for that?"

John held his hand out. "I won't allow this."

"But he was right," said Mycroft, his eyes never leaving Sherlock's. "This is my fault… Moriarty."

"Moriarty?"

"Her Christmas treat: five minutes' conversation with Jim Moriarty five years ago."

"What did they discuss?"

"Five minutes' conversation... unsupervised." Mycroft fixed his suit and smiled. "Goodbye, brother mine. No flowers... by request."

"Jim Moriarty thought you'd make this choice," said Eurus. "He was so excited."

The lights turned back to red as Moriarty appeared on screen once more.

"And here we are, at the end of the line. Holmes killing Holmes." Moriarty smiled. "This is where I get off."

The lights changed again.

Sherlock grimaced, clenching his jaw. "Five minutes. It took her just five minutes to do all of this to us…" He looked at John, then to Mycroft before lowering the gun. "Well, not on my watch."

"What are you doing?" Eurus' voice was panicked.

"A moment ago, a brave man asked to be remembered. I'm remembering the governor." He brought the gun under his own chin. "Ten..."

Eurus frowned. "No, no, Sherlock."

"Nine… Eight ..."

"You can't!"

"Seven..."

"You don't know about Redbeard yet!"

"Six..."

"Sherlock!"

"Five..."

"Sherlock, stop that at once!"

Three small darts shot out of the walls, sticking each man in the neck.

"Four..." Sherlock continued, reaching around and pulling the dart out. "Three…" He was beginning to feel drowsy, his grip on the gun slackening. "Two..."

He felt himself falling backwards. But before his body met the floor, everything went black.

III

"Are you there yet?" Sherlock's voice rang in John's ear, jolting him awake like an alarm clock.

"Yeah, I'm here," he replied quickly.

He was sitting with his back against a wall of slick, cold rocks. It was dark, but he could feel ice-cold water pooling around his waist.

"John!" He could hear Sherlock's voice again, sounding through an earpiece.

"Yeah…" He stood up quickly, his clothes heavy with water.

"Where are you?"

"I don't know. I've just woken up. Where are you?"

"I'm in another cell. I just spoke to the girl on the plane again. We've been out for hours."

"What? She's still up there?"

"Yes. The plane will keep flying until it runs out of fuel. Is Mycroft with you?"

John squinted to look around. "I have no idea. I can hardly see anything. Mycroft? Mycroft?"

"Are you okay?"

"Yeah."

"All right. Well, just keep exploring. Tell me anything you can about where you are."

"The walls are…" he placed a hand on the wall. "Rough. They're rock, I guess."

"What are you standing on?"

"Uh, stone, I think. But listen: there's about two feet of water…" He tried to lift his foot, suddenly feeling something tugging on his ankle. "Chains," he sighed. "Yeah, my feet are chained up. I can feel something."

He bent down, brushing his hands around under the water until his fingers grazed something. He lifted it out, bringing it close to his face to look at it.

"Bones, Sherlock. There are bones in here."

"What kind of bones?"

"Uh, I d'no. Small."

"Redbeard..."

"What?" He waited a moment. "Sherlock? Can you still hear me?"

He closed his eyes and dropped his head as he listened to Sherlock talking to the little girl. He shivered as his wet clothes clung to his skin and continued wading around as far as his chains would allow.

He ran his hands across the walls. They were curved – confined. Tufts of moss and slimy algae decorated every gap in the rocks, and he could hear the faint howling of wind above him. He looked up as a faint glow began to appear overhead – suddenly realising it was not a room at all. Soft, grey clouds drifted across the night sky, revealing a full moon. He looked around again, his vision now illuminated by moonlight.

"Sherlock… I'm in a well. That's where I am; I'm in the bottom of a well."

III

Sherlock raised his lantern to the wall in front of him, noticing a draught blowing gently against the photographs. He looked down at the ground, his brow furrowing at a small gap between the wall and the floor, before putting the lantern down, raising both hands and slamming them against the wall.

The room collapsed, each panel falling to the ground with a hard thud. His eyes widened as he realised he was in a garden, and in front of him stood an old, burnt-out house.

"I'm home," he said. "Musgrave Hall."

"Me and Jim Moriarty, we got on like a house on fire... which reminded me of home," said Eurus through his earpiece.

"Yeah, it's just an old building. I don't care. The plane; tell me about the plane. Now!"

He picked up his lantern and hurried across the grass towards the house.

"Sweet Jim," she continued. "He was never very interested in being alive, especially if he could make more trouble being dead."

"Yeah, still not interested. The plane!"

"You knew he'd take his revenge. His revenge apparently… is me."

He opened the front door and stepped inside. It was a shell of a home; like an empty ribcage that once held a beating heart. He glanced around at the charred walls and dilapidated fixtures as they echoed memories of his childhood like a burnt photograph.

"Eurus, let me speak to the little girl on the plane and I'll play any game you like."

"First, find Redbeard."

In the hallway stood a television. He stepped towards it as Eurus appeared on screen.

"I'm letting the water in now. You don't want me to drown another one of your pets, do you? At long last, Sherlock Holmes, it's time to solve the Musgrave ritual. Your very first case! And the final problem. Oh. Bye-bye."

"Sherlock?" John called through the earpiece.

Sherlock tried to focus on the sound of John's voice, but Eurus' singing made it hard to concentrate.

"Sherlock!"

He ran to a door at the end of the hall and stepped into the room. "John…"

He put the lantern on the floor and rushed to another television mounted on the wall. This time showing John, stuck inside the well, as gushing water poured in from above.

"John? Can you hear me? John! John…."

"Yeah, it's flooding. The well is flooding," he replied, his blunt tone laced with panic.

"Try as long as possible not to drown."

"What?"

"I'm going to find you. I am finding you!"

"Well, hurry up, please, because I don't have long!"

The girl on the plane began to scream. Sherlock closed his eyes for a moment; there were so many voices. Too many. He ran back into the hall. The Musgrave ritual had plagued him since he was a child. He had never been able to find the answer, and eventually, much like every other part of his sister, he had forgotten about it completely. But as Eurus sang the riddle softly, images of his boyhood came flooding back – the salty sea air, the dirt beneath his fingernails, the loyal companion running beside him. Redbeard.

"Sherlock?" John called. "Sherlock… The bones I found."

"Yes. They're dogs' bones. That's Redbeard."

"Mycroft's been lying to you; to both of us," he said solemnly. "They're not dogs' bones…"

Eurus appeared on screen; her vacant expression as empty as the house Sherlock was standing in. "Remember Daddy's allergy? What was he allergic to? What would he never let you have all those times you begged? Well, he'd never let you have a dog! What a funny little memory, Sherlock. You were upset... so you told yourself a better story. But we never had a dog."

Sherlock dropped his head, as his eyes began to well up.

"Victor…" he whispered.

"Now it's coming."

"Victor Trevor."

The smell of sea air grew stronger, the feeling of mud and dirt beneath his feet. He saw a boy on a beach; red-haired and puffy-cheeked.

"We played pirates," he said. "I was Yellowbeard and he was... he was Redbeard."

"You were inseparable. But I wanted to play too."

"Oh. Oh God," his voice shook as the tears escaped down his cheeks."What... what did you do?"

Eurus began to sing again. Softer, slower. "I that am lost. Oh, who will find me. Deep down below. The old beech tree… Deep waters, Sherlock, all your life. In all your dreams. Deep waters."

"You killed him. You killed my best friend."

"I never had a best friend. I had no one."

He raised his head, glaring at the screen. No one.

"Okay," he said. "Okay, let's play."

III

The water had risen to his shoulders. John grunted as he pulled on the chains, trying desperately to free himself. As the well continued to fill, he heard talking in his ear. He pushed his fingers against the earpiece and listened as Sherlock spoke softly to the little girl.

John huffed. "I'm about to drown and you're still bothered about the bloody plane!?"

"I think it's time you told me your real name," said Sherlock in his ear.

"My what?"

"I'm not allowed to tell my name to strangers," the little girl replied.

"Ah, not talking to me. Right. Of course," John muttered as the water rose, forcing him to tilt his head and drink in whatever air he still had left.

"But I'm not a stranger, am I?" said Sherlock. "I'm your brother."

John's mouth fell open. "What the f-!?"

"I'm here, Eurus."

John listened in shock. He could still hear the little girl. But it wasn't a little girl at all.

"You're playing with me, Sherlock. We're playing the game," she said.

"The game, yes. I get it now. The song was never a set of directions."

"I'm in the plane, and I'm going to crash. And you're going to save me."

"Look how brilliant you are."

"Now he's complimenting her," said John. "Great. Just excellent!"

"Your mind has created the perfect metaphor," Sherlock's voice continued. "You're high above us, all alone in the sky, and you understand everything except how to land. Now, I'm just an idiot, but I'm on the ground. I can bring you home."

"No." Suddenly, the voice changed, sending a chill down John's already cold spine. It was Eurus. Undoubtedly Eurus. "No, no. It's too late now."

"No it's not. It's not too late."

"Every time I close my eyes, I'm on the plane. I'm lost, lost in the sky and... no one can hear me."

"Open your eyes. I'm here."

"I'm here too! About seven inches away from drowning, if anyone cares…" said John.

"You're not lost any more. Now, you... you just... you just went the wrong way last time, that's all. This time, get it right. Tell me how to save my friend. Eurus... Help me save John Watson."

"Please!" John shouted.

He was kicking his feet as much as his chains would allow; wading water to keep his head from going under. He groaned in pain as he legs began to burn, the weight of his wet clothes and the shackles on his ankles threatening to drag him under.

He had lost his earpiece in the water, and now, he didn't know how long he had been waiting. No longer able to hear Sherlock's voice, he remained there, with nothing but the sound of gushing water, his own panting breaths and the hope that his friend was on his way.

The water crept below his jaw. He tilted his head back and let out another groan, making one last desperate attempt to pull himself free. Suddenly, a bright light shone down on him from the top of the well. He let out a cry of relief as a rope dropped to him. He clutched it with both hands, his grip slacking from the cold. He clung there for a moment before realising that no one was coming down.

"Well come on then, climb up!" Greg Lestrade shouted from the top.

"Oh, thanks, didn't think of that," John shouted back sarcastically. "I'm chained to the bloody floor you idiot!"

III

The night sky was pitch black, blanketed with stars and the glow of a large full moon. Sherlock stood with his hands in his pockets, his eyes narrow and cloudy as he watched the police escort Eurus away. John stood beside him, wrapped in a thick grey blanket. His hair was damp, dripping down the back of his neck as he looked up at the old, derelict house.

Lestrade approached them slowly. "I just spoke to your brother."

"How is he?"

"He's a bit shaken up, that's all. She didn't hurt him; she just locked him in her old cell."

"What goes around comes around," John added.

"Have you found…" Sherlock began, his eyes falling to the floor as a lump formed in his throat. "Have you found… her body yet?"

Lestrade took in a sharp breath. "Mm. Not yet," he sighed. "But we will. I promise you that. We're still trying to locate her; just waiting on phone records to see where her phone last pinged."

Sherlock nodded.

"Yeah… Give me a moment, boys."

"Oh, erm. Mycroft… Make sure he's looked after. He's not as strong as he thinks he is."

"Yeah, I'll take care of it."

"Thanks, Greg."

John and Greg stared at Sherlock with wide eyes; in all the years they had known him, this was the first time Lestrade's first name had sincerely left his lips.

"Sir!" a young police officer hurried towards them. "Sir, we've found something 'round the other side of the house."

III

Sherlock, John and Greg followed the officer around the back of the house, torches in hand, their breath fogging in front of their faces. The officer shone his torch towards a stretch of land that lead to a woodland far beyond the walls of the house.

He pointed to a heap in the long grass before the trees. "There," he said.

Sherlock, John and Greg lifted their torches, aiming the light where the officer had pointed.

Greg scrunched his face. "Is that…"

"Oh, my god," said John.

Before John could finish, Sherlock had taken off into a sprint. His lungs burned and his tired legs ached as he ran as fast as they could take him. John threw off his blanket and ran after him.

"Margaux…" Sherlock dropped to his knees beside her, placing a hand on her cold, marble-like face.

He winced at the sight of blood on her chest and neck as she lay on her back, the grass glistening dark red beneath her. The hairs on his arms pricked as he touched her. Her body was freezing as a frost began to form across her skin.

John knelt down, his eyes widening at the sight below him. "Oh god," he whispered. "Jesus!" He placed his hand against her bloodied neck in a futile attempt to find the wound.

Sherlock collapsed backwards, sitting in the wet grass as he covered his mouth. A tear trickled down his cheek. Greg threw his hands on top of his head, turning away from the scene and muttering to himself.

She had loved him. Even before she said the words aloud, Sherlock knew. He could feel it, always, in the air between them. He had grown comfortable in her love, revelling in the warmth of her smile, the safety of her presence. He wished he could give it back; hold her in his arms and show her that he wasn't scared anymore.

"Sherlock…" John looked up at him. "Sherlock, I can feel a pulse. She has a pulse. She's still alive…"

He sniffed sharply, his eyes stinging. "What?"

"She's still alive! Greg, ambulance now!"

"I'm on it," replied Lestrade in a panic. He turned to the young officer and began to shout. "Paramedics! I need paramedics here now!"

John locked into action, as if the doctor in him was a mode that he could switch on and off at will. "Sherlock, your coat."

Without a second thought, Sherlock whipped off his coat and handed it to John. Watching as he balled it up and pushed it hard against her neck and shoulder, still unsure exactly where the wound was.

"Margaux, can you hear me?" John asked calmly. "It's John, can you…"

Sherlock leaned over her, cupping her face in both hands.

"Margaux, it's me... I'm here."