The lines are drawn in July, and they show on Marcus' face by the end of the summer. Slytherins weren't made for war, because war means loyalty to power and belief in a cause that isn't necessarily right, that isn't necessarily the best. War means to look out for more than oneself, and that isn't what Slytherins do.
That isn't what Marcus does.
It doesn't matter where they meet because it's not a first, and not a last-- not even a significant number. It might be in the lift and it might be on the street; it might even be in the bakery, at work, at home: premeditated. Marcus doesn't remember because it doesn't matter.
Percy asks, "Have you chosen?"
And Marcus says, "Of course I have." He doesn't need to ask a Weasley, not even Percy, what his choice was. Marcus remembers seventh year, the last one, when Percy whispered, "When the time comes, I hope you're on the right side," quiet and slithering: a threat. Marcus remembers, and calculates, because every little betrayal counts.
It rains throughout August, with water so hot it steams off the streets. London is parched with rain, and Marcus lives in a mackintosh until he stops caring. Stops caring about the water and the damp and the heat, and the war and death and everything. With time comes apathy, and time marches ever on. The rain will stop and no one will notice, just as life does.
He lets rain slick off his jacket and scatter on the marble floors of the Ministry. It will all dry, eventually.
Percy finds him in the drought that follows, and his words dry up just like the sky. The war hasn't touched London and likely never will, but it has touched Marcus and it shows. The ink of his Mark seems to have crept into his blood, staining him ashen, and he no longer looks like the same person that Percy had threatened-- had promised to-- so few years ago.
"What do you want?" Marcus asks, and his voice is tired. Hardly two months and tired already.
"I gave it up," Percy says. He chokes on 'up', like he has only enough breath to shape the word, but not to push it out and away. "I said I would, didn't I?"
Marcus looks at him, heavily, wearily, like he's looking for proof he knows he won't find. "All right," he says, and Percy holds out his hand. Already he can see black trickling into his veins, and soon he will be just like Marcus. He won't be able to hide it.
"I wish you hadn't done that," Marcus says, after some time.
The Ministry closes on the equinox, because the world has gone mad and everyone has let it. Percy stops going in because they stop telling him to, because everyone seems to have forgotten that life does indeed go on, even as the world shrivels and dies.
Percy could pack up, and he could go home, but he has enough reminders of where his loyalties should lie. But he has the hair and the name and the job, and the poverty, and he doesn't need to look his enemy in the eye to know that he's a traitor.
Marcus says, "You're going to regret this," but Percy doesn't think so. Thinks, but conviction isn't going to save him.
"I did it for you," he replies, and Marcus stares. And stares, and stares, and--
"That's the worst reason," Marcus says, "for you to die." And Percy thinks he can see death in Marcus, but maybe it's just the ink.
"Because you will," Marcus says. And Marcus is probably right.