Moriarty couldn't help thinking that Sherlock must be a bit thick to come to one of the most perilous water-falls in Europe, then send John off on such an obviously fake mission, and then on top of all that to cross that rickety walkway, cutting off his only exit. Well…either it was stupidity, or, as Moriarty suspected, it was cocksureness.
Sherlock turned to face him and Moriarty saw, with surprise, a look of fear on his face, and then, contrary to everything he had deduced about the man, resignation. Determined resignation, but resignation nonetheless. Sherlock raised his hand and his eyebrows, whilst at the same time reaching into his pocket. But it was not a gun that he drew forth; it was a piece of paper and a pencil. Moriarty narrowed his eyes, trying to work out what it was Sherlock was up to. But the other simply stood in front of him, paper and pencil in hand, and his eyes were clear, bright and filled with that emotion that Moriarty both loathed – for it had toppled so many of his ambitions – and feared because of the inexplicable strength it gave his opponents.
Sherlock wrote for about a minute, pausing occasionally and pursing his lips in thought. Then, keeping his eyes furtively on Moriarty, he slowly folded the note, stooped, laid it on a stone, took off his watch and placed it, as a paperweight, on top of the note. Moriarty drew his gun, and Sherlock mirrored him. For a second they stood facing each other on the narrow ledge and Moriarty realised, with satisfaction, that although Sherlock had accepted the inevitability of what was about to happen, he didn't have the faintest idea of how it would pan out. So he decided to play with him a bit. Slowly, he placed the gun on the ground and watched as Sherlock's eyes widened slightly. To his reluctant admiration Sherlock, like a good sportsman, took his gun out and laid it down as well.
Moriarty broke the calm, rushing headlong into Sherlock with all his might. The impact was a bit of a shock. He had expected Sherlock to reel back under his weight, but he didn't; therefore Moriarty almost lost his balance. He regained almost instantly however and twisted Sherlock's arm, forcing him out onto the very edge of the ledge. Those sinewy arms were stronger than they looked, and the side of Sherlock's shoe was firmly dug into a rocky groove. No matter how hard Moriarty attempted to topple him, he would not budge.
Suddenly Sherlock's foot slipped, and he instinctively clutched at Moriarty's shirt for support. And at that exact moment, for some arbitrary reason, Moriarty thought of Molly. Maybe it was the method-acting or maybe it was necessity that initiated it all those months back, but now the full force of what it meant to love someone completely and unconditionally hit him like a tidal wave. That was the first revelation, and it shook him enough for Sherlock to regain his footing on the ledge. Close on the heels of this came the realisation that Molly would never, could never requite his love, and that she loved Sherlock. That thought was enough of a distraction to allow Sherlock to slowly manoeuvre himself around so that Moriarty was facing outwards. The second last thought Jim Moriarty ever had was that only one of them could survive, and if he really loved Molly and really wanted the best for her, he would not allow Sherlock to die. With that, he stopped fighting, and felt his centre of gravity shift and his feet leave the ground as he fell backwards into nothingness.
Despite the half-human, wholly instinctive scream that was ripped from his body, the last feelings Moriarty ever experienced as he twisted in space were peace with himself, and, for the first time in his life, the satisfaction of a job really well done.