Marcus is thinking about the havoc and destruction he caused at Megan's wedding, proud of himself that he knew Will would react so predictably. Yet for the first time, Marcus has a nagging sense that something was not quite right. He realizes that his hold over Will is not as strong as it used to be and decides that he needs to get away.
Marcus needs to make a lot money quickly, and the volleyball tournament will have a large crowd, one that he could entertain and make a lot of quick cash. He decides to increase the number of fireballs from six to nine, and orders Blaze to prepare the cloth balls by soaking them in lighter fluid. Neither of them realizes that she is preparing the balls above the shirt she is going to wear in the performance later on.
This short chapter, contrasting with the longer previous one, is important for both character and plot.
Marcus is tired of his "friends" and is going to only look out for himself. This should be no surprise to anyone. What may raise a few eyebrows is his fear of prison. This is an important detail that explains why Marcus needs to act immediately. His feelings of superiority are consistent with the Marcus readers have encountered earlier, and his fixation on making quick, easy money obviously blinds him to what else is going on.
And that something else is the error that Blaze makes while preparing the fireballs. The last sentence of the chapter foreshadows some sort of tragedy for Blaze. Readers know something is going to happen; they just don't know what or to what extent.