On the heels of Tom and Lexi's successful albeit tragic mission to destroy the Espheni power core on the moon, we pick up with Tom's life hanging in the balance as his Beamer drifts into space. While onboard the beamer, Tom encounters a surprising guest who urges him to find his inner warrior. Meanwhile, back on earth, Anne reluctantly steps into Tom's shoes to help lead the 2nd Mass in his absence. Against all odds, Tom makes a miraculous, yet mysterious return to earth. Once reunited with the 2nd Mass, Tom shares a new plan for winning the war. The Espheni, for the first time, are on their heels, and the 2nd Mass will not rest until they are gone from this planet for good.
A surprise skitter attack leaves the 2nd Mass without food. In desperation, Maggie, Ben, Pope, and Sara go on a dangerous mission hoping to find supplies.
The 2nd Mass discovers the source for the seemingly endless supply of enemy forces. With the Volm's help, Tom's leadership begins to spread to remaining human militias around the world. Hal disobeys his father to help Maggie on a personal mission. Meanwhile, Tom has to make an agonizing choice that ultimately risks one of their own, leaving lasting repercussions for them all.
A mission to procure vehicles and fuel goes awry. Cochise shares troubling news with Anne that will test both her medical and leadership skills. Anthony's mental stability and his loyalties are brought into question. Meanwhile, a desperate Pope takes things into his own hands.
The 2nd Mass leaves Chinatown en route to what they hope will be the final Espheni battle. Along the way, they encounter a deranged and desperate gunman who takes Weaver hostage. Meanwhile, Tom sets off to rescue Hal from Pope and his dangerous group of survivors.
Injured, Tom takes refuge with a unique family who has distanced themselves from the fight, giving him a glimpse of life without war. Hal and Isabella's romance grows as they search for a missing Tom. Meanwhile, The 2nd Mass locates an Espheni device that could be a linchpin to winning the war... if they can figure out how to use it. And Maggie makes a decision that has consequences for her and the entire 2nd Mass.
The 2nd Mass arrives at a safe haven. As the two groups make plans for the final assault on the Espheni, the 2nd Mass begins to realize that things aren't exactly as they seem.
Weaver discovers a shocking truth about an old friend and must decide how to best protect the 2nd Mass. Maggie and Isabella are forced to work together, while the remainder of the 2nd Mass attempts an escape led by Tom.
Tom gains a powerful new weapon against the Espheni; Ben attempts to extract enemy plans.
The final standoff brings the Masons, the 2nd Mass and their new allies into the bowels of an iconic American location, wrought with new and unpredictable obstacles. Despite great loss along the way, they must persevere with hopes of once and for all reclaiming Earth and humanity.