Talk about a straightforward title.
Okay, we'll spell it out. The Egypt Game is the game that Melanie, April, Marshall, Elizabeth, Toby, and Ken come up with. That's right: it's a game about Egypt. And at its core is the importance of imagination. The kids transform a weedy abandoned yard into their vision of ancient Egypt, using their imaginations to bring old rituals and gods back to life (at least in their eyes).
So, since the entire focus of the book is on this elaborate game that they've concocted, it's pretty hard to think of a more fitting title. Hollywood-Obsessed April Meets Melanie and They Fight Child Murderers While Using Their Imaginations to Invent the Egypt Game? Nah. The Egypt Game has it covered.