Their eyes meet and their expressions are identical; hopeful and yearning. Sherlock feels his heart clench. He's been a student of human emotion all of his life. He can differentiate between idle interest and consuming desire with a glance. It only takes him a moment or two longer to weigh the evidence and decide if it is lust, or that most complicated emotion of all, love, driving someone's actions. Unwilling to believe the scene that is unfolding before him, he forces himself to study the body language of his closest friend and their most recent client. The clenching feeling grows more intense and he is forced to look away, lest his heart stops beating entirely.
John is thoroughly smitten by Mary Morstan and she is equally enamoured.
When Sherlock walks away, calling over his shoulder that there are details of the case that need to be wrapped up, John replies with a muttered, "I'll catch you up," but makes no effort to turn away from Mary.
When he finally does come home, sauntering through the door a few minutes before midnight, he looks blissfully happy, right up until the moment he sees Sherlock, and then his expression becomes faintly guilty. The next morning, John's apologetic over toast and coffee, but gone again soon after.
The late night arrivals and guilty exchanges over breakfast rapidly become a pattern. When it becomes apparent that this is no side effect of their recent adventure, that the smitten feelings will not fade away like summer sunshine in the face of autumn winds, Sherlock becomes consumed by the doldrums. John is too wrapped up in remembrances of his latest tryst with Mary to notice.
He'd known it would happen, some day. Despite the bonds of friendship and trust they share, despite the intimacy of their relationship, John has needs that Sherlock cannot meet. It is his aloofness that has brought them to this crisis. If he loses John to Mary, he has no one but himself to blame.
That doesn't stop the announcement of their engagement from hitting him like a body blow.
John takes him to dinner, a lad's night out, he says.
Sherlock is glad of it. He misses John's company. Too often John is away from the flat, squiring Mary to art galleries and picnics and meals in restaurants recommended by critics. Often he doesn't come home at all. Sherlock takes on cases he'd normally reject, just to keep busy. He talks to John continuously, even though he isn't there, carrying on as if nothing has changed.
During the meal, John drinks too much, topping his wine glass after every few sips. He's uncharacteristically jumpy. When he finally nerves himself up, he blurts out the news. "I've asked her," he says. "And she said 'yes'. I'm getting married, Sherlock."
Sherlock stares in stunned silence, knowing that he should react.
John finally prompts him. "Aren't you pleased for me?" he asks, and his voice is plaintive. He wants approval, even though he knows it will profoundly change things between them. That his absence from Baker Street will deeply affect Sherlock.
"Yes. Yes, of course," Sherlock stutters back and feigns a joyous expression, smiling although his heart aches. "When is the happy day?"
John replies, but Sherlock doesn't really hear. He's consumed with regrets and eaten with jealousy. These are modern times. If he wanted John, he could have courted him and won him. After all, in some respects, he already has. He considers seducing John when they return home, letting his body say what he cannot admit with words, but he knows it would be a futile act; one they would both regret afterwards.
That night Sherlock uses cocaine for the first time in years. The high is sweet, obliterating the pain he feels in a euphoric burst of energy. John had made assurances during dinner that they would carry on, same as always. But drug-fuelled clarity makes Sherlock realise that is a lie. John won't be around 24/7 to act as a sounding board. His life with Mary will put limits on his involvement with affairs at 221B Baker Street. He won't grumble at Sherlock to stop scratching at his violin at two in the morning. He won't drag Sherlock out of the flat, forcing him to engage with the 'real' world when the black moods try to drag him down. He will become an absence to be missed rather than a constant, reassuring presence.
The cocaine wears off too fast. Sherlock considers injecting again, but puts his syringe and bottle away. He drinks too much instead. He is irritable the next day. And the day after. He feels like a wounded bear and knows only distance will make the situation more tolerable. He takes a case in Monaco and doesn't bother to tell John about it until he is on his way to the airport. He sends a text instead of calling, knowing if he hears John's voice it will only cause fresh pain.
He is brusque with the casino manager and rude to the security staff. He snaps and growls during the briefing. The con that's being run could cost the establishment its reputation. It's already lost their clientèle thousands. They understand that something untoward is going on, but they can't get to the root of how, or who is behind it. They are professionals of many years experience, and clearly frustrated by their inability to find the culprits on their own, but Sherlock can't muster the sympathy to care.
Another pair of eyes is in order. Since calling John is out of the question, Sherlock calls Irene Adler instead. The night life of Monte Carlo should be too tempting to ignore, but she turns him down.
She can't travel at present, it's inconvenient. But she'll be more than happy to chat because, "It's obvious, my dear Sherlock, that you have something on your mind."
She listens as he talks about John and Mary. And then she calls him on the carpet for acting childishly; for trying to have his cake whilst eating it too.
"He needs someone to dote upon him." Irene only confirms what Sherlock knows. John needs to be cared for in a way that is alien to his personality. He tries, from time to time, and knows that John appreciates the effort. But while John will speak up on behalf of others, he seldom has much to say when he feels like his own emotional needs aren't being met. "If you can't or won't, then why not this Mary?"
Her words sting, but Irene's brutal honesty is one of the qualities that Sherlock most admires.
"Just because he loves her, it doesn't mean he'll stop having feelings for you," she says, gently chiding Sherlock's obtuseness. "John has a big heart, and he's more than capable of sharing it with more than one person at a time. Just as you do, when you condescend to admit you have feelings."
There's a subtle note of teasing in Irene's voice and a great deal of affection. It occurs to him that she is speaking as much about their relationship as she is about his feelings for John.
He requests again that she join him in Monte Carlo and once again Irene declines. "I'm not sure that would be wise," she says. "I know it sounds cliché, darling, but you're vulnerable right now, and I don't want to take advantage."
She wants to protect them both. Sherlock is forced to concede to Irene's wisdom. What they share must be separate of any relationship he has with John. Professionally, Irene might have occasionally been the 'other woman', but that isn't a title she's willing to carry into her personal life.
Sherlock goes to bed soon after the conversation ends. He dreams of John, and of Irene, and sleeps better than he has since Mary entered their lives.
He completes his work, enlisting the assistance of a dubious card sharp who owes him a favour. During the course of the investigation he makes amends to the various parties he's slighted, restoring the good will he'd lost and redeeming his reputation as a shrewd yet, efficient operative.
He returns home with his sense of equanimity restored. He congratulates John sincerely on his good fortune, and as they embrace, pounding each other on the back with maybe a shade too much enthusiasm, he realises he's been a fool. No matter what the future holds in store, their friendship will endure.