On the heels of Tom and Lexi's successful (albeit tragic) mission to destroy the Espheni power core on the moon, Tom's life hangs in the balance as his Beamer drifts into space. Back on Earth, Anne reluctantly helps to lead the 2nd Mass in his absence.

When a surprise Skitter attack leaves the 2nd Mass without food, Maggie, Ben, Pope and Sara go on a dangerous mission hoping to find supplies. Meanwhile, Tom and Anne discover the Espheni have created something part Espheni, part Skitter, part Hornet... and part human.

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 across the world, but closer to home, he makes an agonising decision that risks one of their own with repercussions for all.

Cochise shares troubling news with Anne that will test both her medical and leadership skills, whilst elsewhere Anthony's mental stability and 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. 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.

The 2nd Mass arrives at a safe haven - a functional military base run by Weaver's old colleague and flame, Captain Katie Marshall. As the two groups make plans for the final assault on the Espheni, the 2nd Mass begins to realise 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. Meanwhile, Maggie and Isabella are forced to work together, whilst the remainder of the 2nd Mass attempts an escape led by Tom.

Tom gains a powerful new weapon against the Espheni. Ben puts his life on the line to extract enemy plans. Pope discovers that Tom is alive, and launches a final attack. Meanwhile, the 2nd Mass must reassess their situation when an unexpected visitor appears.

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, they must persevere with hopes of once and for all reclaiming Earth and humanity.