Sherlock leans over the back of the armchair, slipping his arms around John's neck and planting a gentle kiss on the corner of his mouth, before he stares at the computer screen, scanning the text and correcting a few mistakes. John closes the laptop screen, turning his head to kiss Sherlock again, before he stands up. The detective follows him into the kitchen, leaning on the counter and drumming his fingers as he watches John making tea. John grins to himself, ducking his head as he moves past Sherlock to the fridge. Sherlock is always more affectionate when he has been to his 'mind palace', something John finds endlessly entertaining, and he tends to stick to the doctor for the rest of the day afterwards. Not that he minds. He leans over the counter to push Sherlock's hair back off his forehead, his eyes sparkling, before the kettle snaps off and he continues with the tea. Sherlock watches his every move, sharp eyes following him around the kitchen until John leaves and he follows a moment later, collapsing into the sofa next to the doctor. He reaches out, picking his violin up, and stretches out across the sofa, and John, starting to play. The tune is simple and sweet, slow to match the speed of John's fingers combing through his hair.
"John? John!" The man with the theatre mask plunges a hypodermic needle straight into the doctor's heart, pushing the plunger before Sherlock rips him off and knocks him out. John stands completely still, his eyes clouding with confusion as he stares down at the needle in his heart. "Sher-" His legs fold underneath him and he drops to the floor. Sherlock kneels next to him, his hands fluttering uselessly over John's chest. It is already painfully obvious that John is going to die, and that there's nothing he can do to save him. He curses under his breath when the doctor convulses under his hands, shushing him gently. "Stay with me, John, keep your heart beating." His voice is strong, while his heart is shattering inside his chest because damnit, John is the first person who made him realise that he is capable of loving someone, and now he's dying in a dingy dressing room in the middle of London. He presses two fingers to John's neck, feeling his pulse grow weaker with every shallow breath. "John, no. John!" John smiles slightly at him, eyes dulling. The beating stops under his fingers and Sherlock freezes. "No, damn you! You are not dying!" Everything seems to be moving in slow motion as he punches the floor, pulls at his hair, yells, and John lies on the floor, broken. Dead.