Clay Riddell, a graphic novelist, is at the Boston airport when a mysterious signal, broadcast over the global cell phone network, turns the majority of the population into murderous, mindless creatures. Desperately trying to survive, Clay teams up with Tom McCourt, a subway conductor, and Alice Maxwell, a teenager trying to find safety. The trio makes their way through the chaos-ridden city, witnessing the devastating effects of the signal firsthand. As they navigate through the carnage and ever-growing hordes of infected people, they bond over their collective desire to find their loved ones and discover the origin of the horrific transmission.

Their journey is fraught with peril as they face constant threats from the phoners – the newly-turned feral humans. To make matters worse, the phoners begin to exhibit flocking behavior and telepathic communication, making them an even more formidable enemy than initially believed. Clay remains determined to locate his estranged son, hoping that the boy somehow managed to avoid the fate that befell so many others. As they travel further from Boston, new allies and adversaries emerge, leading them closer to both the horrifying truth behind the signal and their own limits of survival and humanity.