While out on a scavenger mission Josh and Andy come across a frightened Rottweiler pup, the heart shaped tag on his collar says Rex. Finding anything with breath in its lungs and blood in its veins is a rare thing and the brothers are amazed by Rex’s survival. They take him home and Rex’s presence there makes it easier for them to live in the infected world. In time, Rex ceases to be a pet and becomes the third brother.
Then, early one morning, Rex gets bitten and becomes one of the infected. How will Josh and Andy deal with the turning of their beloved brother?