The promise is made when they're children, eight years old and frightened of the future. Scared to look in the untempered schism, afraid it would reject them, that they would be outcasts from society. The sandy haired boy with excited eyes and windblown hair takes the hands of the quiet dark haired one. He kneels down next to him and the silent one asks his question, "Will you promise me something?"
"Of course" The blond boy replies.
"If something happens, will you stay with me? You'll not abandon me will you?" He voices his fears.
"I promise, I won't leave" He leans his forehead against the others. His young face breaks into a small grin. "Only if you promise the same"
"Of course" He responds confused that the blond could ever have doubted him.
That day comes to an end, they both make it out of there alive, however only one of them walks out of there whole. The dark haired boy who looked into that rift with frightened eyes walks out of there with something else. Inside his head hidden away, where it will one day come to light, the drum beat that calls him to insanity.
They get older and they stay the same. The two best friends that ever were, inseparable is the word most often used to describe them and it's something that their teachers wish wasn't the case. They are notorious, the most intelligent students to ever enter the academy, and the two biggest trouble makers in history. Whether it's sneaking out of lessons to run across the fields, or it's making up stories of their epic battles against the monsters of the universe they do it together. They keep their promise to each other. When the blond breaks his ankle falling out of a tree during their adventures the dark haired boy runs to his side and half carries him all the way back home. That night when they get home, his parents yell at him for being so reckless and he is sent to his room, while the dark haired boy is asked to leave. That night he climbs through the other's window and sits next to him. They're teenagers that night when he say "I promised didn't I?".
Neither of them ever forgets any of their adventures. Both of those brilliant boys remember every moment under the light of the red sun running through the citadel, every minute spent under the twin moons, counting the stars and telling each other which ones they'll go to.
He's just become an adult the day he finds her unlocked and oh so inviting. He's just completed the final part of his training, he is now ready to take on the universe after deciding on his name. His best friend is still in the room. He's been let out into the hall with all those beautiful machines knowing that now he stands a chance of maybe one day owning one. He lets out an excited breath. And from behind him, he hears a machine sigh in sync with him. He whirls around, his blond hair flying and there sitting there with the door left open just a crack, is the most beautiful thing that he has ever seen. For once the dark haired boy he grew up with is far from his mind and he enters that glorious console room for the first time. He reaches one hand out and touches it so gently like he could break it all with one false move. She reacts to him and slams her door shut and whirls him away through time and space. He thinks of the dark haired boy, wants to show him the magic he found.
But the other boy remembers the day differently; he had run out of their desperate to see the other. Only to find their meeting point empty. Only, to wait for hours expecting his friend to return, bursting through the doors and tell him where he'd been. There he sat for hours wondering about the name he would choose. He needed something strong, something that showed what he was. He wanted to ask the sandy haired man what he thought of it. He needed his best friend's approval before embarking on this journey. For a week he waited. Sitting there in that silent room waiting for his friend to come to that appointed meeting place. Eventually he walked out of there turning his back on his friend and walking away down the corridor, eyes lighting with a dark emotion, hatred. It's been two months that he's waited. Two months since his friend vanished without a trace only a missing TARDIS.
When the fair haired man arrives back it's with flushed cheeks and an excited grin, he throws himself out of the door ready to take his friend on wonderful adventures. But the room is empty, he wonders through the citadel, ignoring people calling to him in shock. He wonders if his friend is injured or unwell, why else would he have not been waiting. When he finds him, his young friend is dressed all in black with his back turned. He starts forward, launching at a mile a minute explanation of the adventure he has just had. His friend doesn't turn. A puzzled look crosses his face and he reaches out a hand and says his name.
Quick as a viper, the dark haired man turns and corrects him. "It's the Master now" He says curtly. Confusion flickers on the blonds face. "And don't act like you care. You left"
"But I came back" His friend counters.
"A little late don't you think?"
"What do you mean?"
He honestly wants to believe those innocent eyes and startled look, but he reminds himself that this is the same person who left him for so long. "Two years, is too late, even for us" He walks away, telling his once friend nothing of all the times he cried himself to sleep begging for his return, nothing of his father's death and his mother's suicide. It's on that day that the Master walks away with the drums sounding in his head.
The sandy haired man lets the shock stop him from running after the dark haired friend. It is in that moment that he thinks of his name, what he wants to do with his life. The Doctor, healer of the sick. If only he could heal his friend. He'll go out there and heal the universe if that's what it takes to heal the Master.
The promise made as children breaks on the day they become adults. And their friendship which had shown with happiness shatters into fragments that can never be completely fixed.