Mankind is no longer at the top of the food chain. The Sixth Extinction is an apocalyptic tale about a pandemic that sweeps the globe, decimating the human race, leaving humanity struggling to survive. Within three weeks, everything has changed. Social structure has collapsed as the government locks itself away with a select portion of its vast army in deep bunkers, leaving the civilians to their own fate and the infected that stalk the streets. Alex, Troy, Tierra and her son, Naomi, and the two King brothers are trying to find somewhere safe to survive, but people are dying at every turn, and there are now only seven of them left. They narrowly escape an ambush by Stitt and make their way to a gas station next to a river swollen by a torrential storm. Exhausted, hungry, and in shock at losing so many of their companions, they try to settle for the night, only to be attacked by a horde of infected that pours across the fields surrounding them. However, it appears the creatures were drawn by something else. Out of the darkness emerge other uninfected humans. They come to the rescue, fighting like people possessed. They travel the river in an old fishing boat, looking for supplies and other survivors. Also, they are in possession of a secret that could save them all. Meanwhile, Doctor Bachman, and the two lab assistants, Emma and Peter make their way to the supercomputer in Zone 12, while keeping their distance from the tentacled creatures and pods that stalk the bunker. They plan on using a fail-safe system called The Furnace to wipe the creatures out. But first, they have to navigate through the sewers to get there, and while doing so they come face-to-face with their worst nightmare. Have they got what it takes to reach the supercomputer in time before six new strains of the infection spreads into the atmosphere?