"He's got my whole life story. That's what you do. You sell a big lie. You wrap it up in a truth to make it more palatable." Sherlock paced up and down the street, growing increasingly agitated as his mind worked at an increasingly faster rate.

"It's your word against his," said John, who was still half-concentrating on the papers documenting Moriarty's own fabricated life story.

Sherlock began to dismiss John's comment instantly, before stopping mid-deletion to ponder it. What he'd told John back at 221B Baker Street was true: he didn't care what other people thought. He knew the truth, he himself knew what was fact and what was fiction,and that was all that mattered. Wasn't it?

"He's been sowing doubt into people's minds for the last 24 hours. There's only one thing he needs to do to complete his game and that's to..." Sherlock paused here as the final piece of the puzzle slotted into place while he spoke, as his mental deductions occurred faster than his mouth could physically speak. "There's something I need to do."

"What? Can I help?"

"No. On my own."

Stupid. Stupid. Obvious! Sherlock chastised himself as he walked away from John, leaving the confused doctor behind. Belatedly, Sherlock had realised what the final stage Moriarty's game was.

It was clear to all involved now that Moriarty was trying to destroy Sherlock's reputation, that Moriarty had made it his personal goal in life to discredit and shame him, and make Sherlock out to be the fraud that those closest to him knew that he wasn't.

This would be the final stage of Moriarty's game, to have Sherlock's reputation shattered into a million pieces so that nobody would ever consult 'the world's only Consulting Detective' with their cases or intrigues again. This - not John, after all - this was the 'burning of Sherlock's heart' that Moriarty had alluded to. If it was successful, then Sherlock's mind would be tormented, left to stagnate, and to rot away with boredom just as Moriarty's own mind had begun to.

The boredom, the constant lack of a lasting challenge for Moriarty's brilliant mind was slowly destroying him. Everything had become too easy for Moriarty to achieve now. It had all become too predictable, and now that Moriarty thought that he was one step away from causing Sherlock's 'fall', the 'Consulting Criminal' would be reckless and more dangerous than ever, having nothing else to strive for now that he had as good as already caused the demise of the only other mind that could have posed any sort of challenge to, or for, him. Moriarty was bored, and Sherlock knew what boredom could drive a person to doing.

At the pool, when Moriarty had first threatened to 'burn the heart out of Sherlock', Sherlock had - mistakenly, he now realised - believed that Moriarty had been referring to John, that Moriarty had been threatening John's safety, believing the doctor to be Sherlock's 'heart'. In Sherlock's defense, it had been a logical conclusion for him to make back then, having accidentally revealed to Moriarty that he cared for John through his reaction to seeing the doctor strapped to an explosive device of Moriarty's design.

With hindsight, it was easy for Sherlock to see that he had made a fatal error by allowing this sentiment to cloud his judgement back then. If, at the pool, he had managed to ensure that his thoughts remained purely logical, and that he only deduced from the evidence that he himself could see, then Sherlock would have realised his error. John had only been taken to get Sherlock's attention, not because Moriarty had realised that there was some kind of bond forming between the two flatmates.

When Sherlock thought back to his conversation with Moriarty at the pool, he recalled hearing Moriarty say that Sherlock would have to be stopped, that he had interfered with Moriarty's plans too many times to be allowed to live. However, the only thing that an emotionally-compromised Sherlock had managed to ascertain was that John's safety had been threatened because of him. John, the only person to tolerate him for who he was, and who had never tried to change him. Amazing, brave and loyal John, who - only hours earlier, back in the present day - had told him that he knew for certain that Sherlock was no fraud.

Back then at the pool, Sherlock had felt guilty, apologetic and apprehensive, whereas he now realised that he should never have let himself feel anything at all.

Thankfully, the confusion over what truly was Sherlock's 'heart' had allowed Sherlock to realise that Moriarty still had no comprehension of Sherlock's feelings for John. Moriarty could be forgiven for thinking that The Work was Sherlock's heart at the pool, because Detective and Doctor had not known each other long at all. After all, their loyalty to each other had never been tested that strongly before.

But now, now that Moriarty had seen them together, had seen how much the two needed each other and still failed to adjust his Plan accordingly, Sherlock could deduce Moriarty's own downfall. Moriarty still believed that The Work was Sherlock's heart, and this had finally proved to be the difference between Moriarty and Sherlock. They weren't as alike as Moriarty had thought - or as Sherlock had secretly begun to dread - after all. The difference stemmed from the fact that Sherlock claimed to be a sociopath: an impulsive, irritable and irresponsible individual with a tendency to lack remorse for inappropriate actions, or fail to conform to social norms. A person who used deception willingly to achieve their own ends.

Maybe this was true, maybe Sherlock actually was the sociopath which he professed to being. But maybe, just maybe, he wasn't.

Regardless, the difference between Sherlock and Moriarty was that - although there may be doubts around Sherlock's diagnosis as a sociopath - there could be no doubts around Moriarty's diagnosis. Moriarty truly was a psychopath. It was highly unlikely that he was afraid of anything, he was impulsive, and his high self-confidence in even the most dire situation was alarming. Also, Moriarty had proven on more than one occasion that he could not form, and lacked the ability to empathise with why people would want to form, any true, deep or meaningful relationship or connection with anyone.

Because of this, because of Moriarty's inability to understand why people formed such strong attachments to others, Moriarty had failed to grasp what Sherlock's 'heart' was. Moriarty couldn't comprehend matters of the heart, and so he had fallen victim to the lie which Sherlock professed to the world, which was that 'all that mattered to him was The Work'. It seemed that sentiment would cause the downfall of a great mind again, but this time it would be a lack of sentiment which did it, and not the possession of it.

Moriarty's aim was to ensure that Sherlock was publicly disgraced and discredited. By doing this, by destroying Sherlock's reputation, and by destroying everyone's faith in him, it would render Sherlock unable to do the work which he craved to give his mind peace. In Moriarty's eyes, what could possibly be a better way to burn the heart out of Sherlock Holmes? Sherlock Holmes, the man who was so consumed by his work and by a longing for something to challenge his intellect, that he had failed to observe what was staring him in the face.

But now, now that Sherlock finally understood Moriarty's motive fully, he could begin to do something to stop him before anybody else could be harmed because of their 'Great Game', and his own stupidity.