When James Moriarty was young, he had an imaginary friend. The Doctor, he was called, and he was wonderful. He was a time lord, a warrior who fell from the sky and tore down worlds. Until he met the Doctor, Jim had actually believed that one man couldn't accomplish anything. He knew differently now. He had had a glimpse at a whole new life with the Doctor, and it was then he'd decided - Jim would spend the rest of his life recreating his imaginary friend's footsteps.
He'd started with his class bully, Carl. The bigger boy had been pushing Jim around for weeks, stealing his lunch money and laughing at his inability to retaliate. The day after his adventures with the Doctor end, Jim walks into school with a quiet confidence he'd never possessed before. He bides his time, watching the formerly overpowering and bullish boy become less so every day. There is not one shred of doubt in his mind that this is the best course of action. If he had considered the situation, he would have concluded that the Doctor would have been proud of him. He was taking control, defending himself - he was strong, one of life's victors. The day he hears of Carl Powers' death is the best day of his young life.
Jim's next taste of death is his university professor. The man is as boring as he is foolish, and there is nothing Jim detests more than a dull idiot. Not only that, but his failure to recognise the brilliance of his pupil at every turn is a constant irritation. An incompetent professor will not mar his career, Jim swears it. Years later he will look back on his second kill as clumsy, but at the time it appeared to him to be the most elegant of solutions. An economics professor asphyxiating as a result of coins lodged in his trachea - the irony of the death was so beautiful to him. Suspicion never falls on Jim - already he has the skill of disappearing into a crowd. He savours the power of life and death, present in his own hands. His imaginary friend would be so proud.
As Jim grows older, he absents himself from the truly dirty work. He prefers to orchestrate the chaos, rather than participate, viewing himself as the omnipresent deity. It pleases him to think of how closely his work resembles that of the Doctor's. Like his friend, he can destroy worlds with a single word. He has a flair for what he does, and what's more, he truly enjoys his work. Jim has finally become the man he had always dreamed of being, and he thinks it is about time he outgrew the shadow of his imaginary hero.
Then the Doctor returns.