Mars Bar and Maniac used to both jog in the morning, and since they both are in the same place they start to jog together.
Maniac and Mars Bar jog together every morning. At first, Maniac thought he heard someone else’s footsteps, but was not sure. Then he realized it was Mars Bar, but neither boy said anything. They just were in the same place at the same time, seemingly by coincidence.
Although the two never speak, they actually are in tune with each other.
Though each face showed no awareness of the other, they were in fact minutely sensitive to each other. If Mars Bar cranked up the pace just a notch, Maniac would pick it up within a stride; if Maniac inched ahead, Mars Bar was there. If one veered to the left or right, the other followed like a shadow. (Ch. 44)
The two boys run together until they reach the end of the route, and then Maniac goes one way, and Mars Bar goes to his neighborhood. Again, there is no communication or plan to meet. They just meet.
When the working people began leaving their houses, the daybreak boys diverged, Mars Bar to the East End, Maniac to wherever. A week passed. A second week. Morning after morning. Stride for stride, breath by breath. Never a word, never a glance. Each believing the other simply happened to be going where he was going. (Ch. 44)
This is how Maniac and Mars Bar are together when Piper comes to them to tell them that his brother is in trouble. The boys were playing on the trolley trestle when Russel froze, afraid to move back. Manic does not want to go out on the trestle, because of the way his parents died.
Mars Bar saves Russel, even though he is white and Mars Bar is black. He was a boy in trouble, and that was all that mattered. Maniac’s attempt to bind the races seems to be working.