Nick goes to visit Marie's sister, Natasha, and learns that Alan has been keeping more secrets from him than he suspected.
It turns out that this woman, Natasha, was the one who wrote all those letters to Alan last year, and that the girl in the picture, Marie, was Alan's mom.
Nick is surprised by this, but it makes sense. He even kind of gets why Alan kept it secret—he didn't want Nick to know they had different mothers.
But then Natasha insists that Daniel Ryves can't be Nick's father, and he realizes she's right. He puts two and two together and realizes who his real father must be.
Nick drives back to London, where the car breaks down on Tower Bridge; Nick abandons it and walks home in the rain.
He doesn't get there until 3:00AM, and everyone's worried about him, but when Nick sees Alan he flies into a rage. He tells Alan he knows everything, including the fact that Black Arthur is his father, which, he says, makes sense. Nick is, after all, really good at killing.
Alan tries to explain why he kept everything secret, but Nick is too angry and he punches Alan, at which point Alan draws his gun.
After a few more angry words, Nick calms down and tells Alan not to worry. He knows Alan saved his life—and his mother Olivia's life, too—and he'll repay him. He'll catch a magician and get Alan's mark removed and then they'll be even. And after that, he never wants to see Alan again.