It is related and some of the characters were in the first book in the series, No Easy Hope. It is more of a supplemental reading to the series.During the Outbreak, like billions of others, a man finds himself infected with the Phage. Desperate to spare his family from watching him become a walking nightmare, he flees. Soon after, he is dead. Two years later, he wakes up. Not in the afterlife, but in his own body. Trapped, unable to control the monster that carries him, and forced to witness the horror of its existence. A hundred miles away, Sergeant Ethan Thompson thinks he has seen the worst the apocalypse has to offer. He is wrong. Following the trail of a dying madman, he will embark on a journey of vengeance that will test the limits of his sanity. Along the way, he will learn that there is no justice at the end of the world. There is only the living and the dead, and in between, there is The Passenger.

    Unfortunately, that "normal" includes collapsing skyscrapers, bands of bloodthirsty maniacs, and a dwindling cache of survival supplies. After watching his family, friends, and most of the non-sadistic elements of society crumble around him, Patrick decides it's time to cross one last item off his bucket list. He’s going to Disney World. This hilarious, heartfelt, gut-wrenching odyssey through post-apocalyptic America is a pilgrimage peppered with peril, as fellow survivors Patrick and Ben encounter a slew of odd characters, from zombie politicians and deranged survivalists to a milky-eyed oracle who doesn't have a lot of good news. Plus, it looks like Patrick may be hiding the real reason for their mission to the Magic Kingdom...

    In Los Angeles, Raymond and Mia James are about to lose their house. Within days, none of it will matter.When Vanessa dies of the flu, Walt is devastated. But she isn't the last. The virus quickly kills billions, reducing New York to an open grave and LA to a chaotic wilderness of violence and fires. As Raymond and Mia hole up in an abandoned mansion, where they learn to function without electricity, running water, or neighbors, Walt begins an existential walk to LA, where Vanessa had planned to move when she left him. He expects to die along the way.Months later, a massive vessel appears above Santa Monica Bay. Walt is attacked by a crablike monstrosity in a mountain stream. The virus that ended humanity wasn't created by humans. It was inflicted from outside. The colonists who sent it are ready to finish the job--and Earth's survivors may be too few and too weak to resist.