Grim thinks it's from carrying "poor Kevin around." But Max tells him he's not that heavy. Also, he doesn't understand why people keep calling him "poor Kevin." Kevin is smarter than most adults he knows. Is there something Max doesn't know?
Before Max can think too much about this, Freak shows up with a Quest. He's found something in a storm drain nearby, and they decide to wait for the cover of darkness to go find it.
Meanwhile, they make their preparations. They look for soot to cover their faces, but since this isn't 19th-century England, they have to settle for dirt.
They wait till 3:00AM and then sneak out, Freak all decked out in a Darth Vader costume. We mean, come on. What else would he wear for a quest?
Together, they make their way to the storm drain. Max pulls off the grate, and they fish out a woman's purse. Max is not impressed: "It looks like a grotty old purse" (10.71).
Freak explains that he saw one of Tony D's gang throw it in there. He must have stolen it.
They find a wallet and decide to return it to this damsel in distress.
Only later do they realize that this is no damsel in distress, but rather a "damsel who causes distress" (10.84).