The lock showed no trace of forced entry.

Sunlight glinted off the sign displaying 221B as Sherlock swung the front door open, quickly scanning the familiar surroundings. Nothing out of place. He let out a deep breath.

And then he heard it.

A violin's sweet melody drifted from upstairs, hanging lazily in the still air. It took him only a second to identify the tune: Partita No. 1, Johann Sebastian Bach.

His blood turned to ice.

Woodenly, he forced his feet to move, one step at a time, shuffling on the carpeted floor. The music continued, chords stretching lovingly, almost invitingly.

His foot hesitated on the first step.

You can do this.

He shifted his weight, placing both sweating palms on the wooden railing for support. Breathe. Breathe. He swallowed, closed his eyes. Don't be afraid.

Step. Breathe. Step. Creak.

The violin – his violin – faltered. His heart leapt to his mouth; his muscles seized up, freezing him into place.

A second later it resumed playing – like he knew it would.

He shook his head sharply, curls bouncing, and made a decision.

To battle.

Although he'd known full well what awaited him, a shudder still ran through him at the sight that greeted him as he opened the door.

Moriarty stood poised, the violin tucked under his chin, fingers dancing on the strings while his other hand worked the bow in long, sweeping, fierce movements. His back was turned but Sherlock could see his profile: the perfectly sculpted eyebrows, angular nose and plump lips which he suddenly realised he'd long committed to memory. The man's eyes were closed in bliss as the majestic notes thrummed from the instrument – and slowly opened as they died away, acknowledging his enemy's presence.

He lowered the violin, breaking into a teasing grin.

"Ah, Sherlock," he purred. "A pleasure to see you in the flesh again."

The detective's jaw was clenched tight, posture stiff. This man is your enemy, he reminded himself. Don't trust him. Don't ever trust him.

Jim languidly returned the violin to its case, snapping it shut. "Did you like my little rendition?" he continued, dark eyes flickering over to meet Sherlock's. They bored into him like blackened pits, disconcerting against the alluring smile. "I've had over two years to learn. D'you have any idea how boring it was for me, Sherlock?" He gave an exaggerated cringe. "You couldn't even be bothered to see if I was alive! Tut, tut…" He sighed heavily, shaking his head in mock disapproval – then paused, and let the condescending grin creep across his face again. "Too afraid to find out?"

I am not afraid, Sherlock wanted to spit out, but the words died on his lips.

Because Moriarty was back – he was right there in front of him, wearing the same grey suit he'd worn at the trial, dark hair slicked back, darker eyes blinking with the same false innocence. There was no denying it. Not even his singsong tone had changed. It was almost as though the past three years had never happened at all. And Sherlock didn't understand – why he was here, how exactly he'd survived, how to resolve their rift – and above all, how the criminal's reappearance made him feel.

You hate him, his mind repeated, over and over: You hate him, he's dangerous, unpredictable, unexplainable; he's a murderer. You hate him.

But he could tell the attempts were half-hearted. And that was what confused him the most.

Focus, focus. He blinked hard, clenching and unclenching his fists, bringing himself back to face Moriarty's unwaveringly smug features. Concentrate on the task at hand.

"Wh… why are you here?"

Was that really his voice? So weak and thin and frail? He swallowed again, flexed his fingers. Lifted his chin a little higher. Stay strong.

Jim took a deep breath, spread his hands, and – for a split second – his smile almost seemed… genuine.

"To thank you, Sherlock."

Thank me? Whatever Sherlock had been expecting, that wasn't it. He struggled to keep his expression neutral. "Thank me… for what?" His speech was sluggish, and he gave himself a mental slap. Focus.

Moriarty glanced around the room, scanning it, before letting his gaze settle onto where John's chair used to be. "Shame you got rid of that," he drawled, ignoring Sherlock's question. "Quite petty of you, isn't it? All this moping after Johnny-boy." He flicked imaginary dust off his suit sleeve. "I should pay him a visit sometime. The Watsons… they're having a baby, aren't they?" A smirk. "Now that should be interesting."

Don't you dare go anywhere near John. Don't you dare even look at him. But all that spilled from his mouth was, "I'm not moping."

Jim rolled his eyes. "Whatever you say, darling Sherl. Oh wait, wasn't that what Janine called you?" He laughed, as though reliving an old memory. "That was downright cruel, Sherlock, what you did to her! Still, I'm one to talk." Shaking his head, he cleared his throat before taking an elegant step backwards, a dancer before an audience, gesturing to the one remaining armchair. "But where are my manners? Sit."

"What did you mean… thank me?" Sherlock tried again, not moving a muscle.

Jim's eyes flashed dangerously. "Sit down," he repeated, an edge of steel to his voice, "and I might juuuust tell you."

The detective could disobey no more. Frowning, he tried to ignore Moriarty's relentless stare and made his way awkwardly to the armchair, perching stiffly upon it. He kept his hands folded in his lap.

"Thank you!" Jim beamed at him rewardingly, before hopping onto the wooden table to sit there himself. He began to swing his legs in the air as he spoke. "So DIDyou miss me?"

"No," Sherlock replied immediately, despite his mind screaming otherwise.

Jim pouted. "Oh, don't be like that. I'm back, aren't I?" He reached into his suit's inner pocket and carefully plucked out a rose hidden there. With a flick of his hand, he tossed it towards Sherlock; its appearance had startled him and he struggled to catch it. Jim laughed and continued. "I evaded death for you. You don't get much more romantic than that."

"You pretended to cause your own death for me in the first place." He found he was stroking the crimson rose petals – and, strangely, let himself continue.

"Are you arguing with me, Sherlock?" Moriarty widened his eyes and shot a sudden, fierce glare at his opponent.

Before Sherlock could stutter out a N-n-no, the criminal threw his head back and burst into merry laughter. Sherlock stared at him, dumbfounded.

"Oh, I did miss this!" There were tears in Jim's eyes. "No-one else would dare speak to me the way you do. Oh, Sherlock…" He pursed his lips and took a long, exhilarated breath.

"Look, why are you here?" Sherlock's heart was racing again and he needed this over with. "What do you need to thank me for?"

Moriarty sighed heavily, the smile fading. He glanced around him again, then tutted quietly under his breath. "You had tea last time."

"Last time, I actually had time to prepare it."

"Ah well. Let's just call the landlady." He raised his voice suddenly – "MRS HUDSOOON!"

"Shut up! What are you doing?!" Sherlock gasped, hastily calling out, "No, Mrs Hudson, it's – it's fine, ignore us!" His voice reverted to an icy hiss as he glared at his smirking enemy. "Are you insane?"

Jim pondered the question for a moment. "Prrr-obably."

"Just…" Sherlock let out a deep breath. "Answer my question."

"I just did."

"The other one!"

"'What am I doing'? Well, I'm calling the landlady so we can have some teeea." He swung both legs up and down at the same time, childishly.

"I meant–" Sherlock rubbed his temples, soothing his irritation. You can't piss him off. He's the most dangerous man on the planet. "I meant, why are you here?"

The leg-swinging stopped. Jim glanced down at his hands. If Sherlock didn't know better, he'd say the man looked positively… anxious.

"Sherlock…" he began in a low voice, swallowing and looking up – not meeting the detective's gaze. "You and your friends weren't the only ones Magnussen was after."

What?

"I'm the king of the criminal empire, Sherlock, what do you expect?" Jim's tone was unexpectedly tender, as he sat glancing at and away from his rival's dumbstruck expression. "Someone like Magnussen would do anything he possibly could to control me."

"But…" Sherlock shook his head disbelievingly. "What could possibly matter enough to you for him to blackmail you with?"

Jim sighed deeply. "Once again, you underestimate us." He met the detective's gaze – and held it. "You have all your 'pressure points', as he and I put it. What makes you think I'm not the same?"

Sherlock fell silent.

"Don't think you're my only enemy," the criminal continued. "You're my favourite, of course, but there are so many others… more ruthless, cold-hearted and far more stupid." He leaned forwards. "And I have secrets they can't ever know."

"What secrets?" Sherlock searched his opponent's gaze, but the deep, dark eyes shed no light upon the nature of his soul.

The smile crept back onto Moriarty's face. "Oh, if you're good, I might tell you."

Sherlock blinked, frowned, looked away: feigning nonchalance. Jim smirked and drew backwards, dangling his feet.

"So my… removal of Magnussen enabled your return?"

"It eliminated one of the main problems." The sombre expression returned; the feet stilled. "So… thank you, Sherlock." He blinked, voice softening; he looked almost… proud. "I knew you had it in you."

Warmth spread in Sherlock's chest; he swiftly combated it with an icy tone. "I didn't do it for you, James. I did it for Mary." And for John.

"Doesn't mean I can't thank you." A hard look crept into his eyes. "And you know it's just Jim, not… James." As the detective made a move to stand, he swiftly raised a hand to stop him. "No, Sherlock, please stay. You and I aren't done yet."

"What do you mean? I accept your 'thanks'. Now–" His chest squeezed uncomfortably, but he shoved the feeling aside. "Leave."

Jim shook his head with a finality Sherlock couldn't ignore. The detective leaned back in the armchair and sighed, pretending not to notice his pulse spiking.

"Have you got any cases?" Moriarty asked, almost casually.

"Plenty."

"Liar." Now it was the criminal who stood, smoothing out his expensive suit. "You've been too busy worrying about your imminent deportation and death. Now John's gone–" Sherlock winced– "and soon you'll be bored out of your mind. But…" He took a step closer. "I can help."

"What, another of your little games?" Sherlock forced boredom into his tone, lifting his chin to stare defiantly at his slowly advancing enemy. "You run around killing people and I chase after you again?"

"No, Sherlock." Suddenly, Moriarty knelt, crouching down before the consulting detective – leaving their faces mere inches apart. Gently, he placed a hand onto Sherlock's knee; his shadowy gaze was unflinching.

"I want you to solve my case."

The blood began to thump in Sherlock's ears.

"Solve… your case?" he repeated slowly. The hairs prickled at the back of his neck. The hand on his knee was unbearably warm. Don't think about that. Focus. Focus.

"Yes," Jim murmured, his gaze unflinching. "I need your help."

The words echoed all over Sherlock's mind.

I need your help…

"H-how…" The sheer intensity of the look in Moriarty's eyes made him stumble breathlessly mid-sentence. I need your help – what was that supposed to mean? He swallowed hard. This is a trick. Don't let it get to you. His hands trembled in his lap, itching to do something – but whether that was to push Jim away or pull him even closer, he didn't know.

"How," he breathed, the words forming at last, "could I possibly help you?"