Forty-two days have passed since the monsters attacked the city. Almost all the residents have disappeared—either they left or became zombies. However, a typical thirteen-year-old boy, Jack Sullivan, is hiding in his treehouse, which is surrounded by a moat. He is armed with a catapult and video games, and has endless supplies of cookies and sodas, which he has procured from the city's abandoned stores. However, Jack cannot face the hordes of lurking monsters alone, especially the relentless threat known as Blarg. He must find allies, other kids or monsters who will trust him. With their help, he will fight to crush Blarg and become the ultimate hero of the new era!