Mars Bar became Maniac Magee's running partner.  One evening, "Maniac thought he heard footsteps other than his own" while he was out running. He looked all around, but he did not see anyone else. This happened again, and then again. Maniac began to sense that someone else was running near by. Finally, one morning Maniac turned a corner and collided with another runner. He was surprised to find that it was Mars Bar Thompson!

Maniac and Mars Bar had gotten in an argument not long before. After their running collision, they both ran off in different directions.  For awhile, the two boys had random mergings while on their separate daily runs. Eventually, they began running together for a block or two. One day, they started running together the whole time. They followed each other's lead on their runs:

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.  One day one was the leader, the next day the other.

The two boys continued their morning runs each day. They never spoke to each other while they ran. They never even looked at each other intentionally. They just ran.