As John and Sherlock approached Greg's office, they heard body-wrenching coughing that seemed to drag on forever. The detective frowned, looking at John, and opened the office door without knocking.

"That sounds less than good," John said as he shouldered his way around Sherlock. He stepped up close to Lestrade and pressed his hand to the DI's forehead before the man could protest.

"I'm fine, John," Greg choked out between coughs. "It's just bronchitis."

"Just bronchitis," the doctor said dryly. "What are you taking for it and why the devil are you at work?"

"Really, I'm fine. I'm on antibiotics, so I'm not contagious," the DI said defensively.

Sherlock leaned over Greg's desk and picked up the DI's pack of cigarettes. "I told you once, these things will kill you. This is your third case of bronchitis this year. Don't you think you should give them up?" He dropped the pack to the desk. "Or would you rather develop COPD?"

John laughed. "That's a bit... pot, kettle, don't you think?"

Sherlock pressed his lips into a thin line as he considered. After a moment, he reached into his pocket and pulled out his own pack of cigarettes. He used his long fingers to extract a single fag and twirled it in his fingers. "Once, there was a young man, almost a kid, really." Sherlock snapped the cigarette in two. "He was highly intelligent, so intelligent, the world despised him for it, mocked him and locked him out in the proverbial cold." Another cigarette was snapped. "That man made an idiotic mistake and turned to drugs for comfort. At first, it made his mind sing, everything was so clear and he could see things others couldn't." Snap. "But that changed. The cocaine highs turned dark, his mind still sped, but the euphoric feeling eluded him." Snap. "He used stronger and stronger dosages until, one day, he suffered an overdose. Were it not for the timely arrival of a police sergeant, the man would have died." Snap. "That same sergeant offered the man a deal: get clean, stay clean and he could help the sergeant on interesting cases." Snap. "It had to be off the record, but the young man didn't mind. It's been almost nine years now and that young man has managed to stay clean." Snap. "I think you can manage to quit smoking. If you do, I will." Sherlock held the last cigarette in his fingers. He closed them around it and crushed it.

John and Greg looked on in stunned silence. Silence that was broken by the DI's strained, wheezing cough. When he had recovered, he looked at Sherlock long and hard. "After all this time, you're telling me you care?"

"I did no such thing." Sherlock wrapped his Belstaff around him tightly in apparent indignation. "I simply told you a story, made an observation and offered you a challenge. It's up to you if you take it."

Greg picked up his pack of cigarettes and looked at them. "And if I don't?"

Sherlock shrugged. "COPD within five years."

The pack of cigarettes were swiftly crushed in Greg's tight fist. "Challenge accepted," he said with a cough.

"Good. Now get me the files for the case," Sherlock ordered. "I'll solve it and you can go home to get some rest."

"They're in the incident room. I was just taking a break." Greg stood to leave his office. "Come on. You can see everything there."

With a hand on Sherlock's arm, John stopped him. He went up on his tiptoes and kissed the detective on the lips.

"What was that for?" Sherlock asked, bemused.

John smiled. "For being you."