The world is left in tatters after a sudden, unprovoked and unexplained invasion by aliens, leaving the planet’s remaining human population to fight for survival against the occupiers. History professor Tom Mason has been named second in command for the 2nd Mass, but his real focus is on his three sons, one of whom has been captured by the aliens for an unknown purpose.
While scouting for supplies, Tom, Hal and their squad encounter a gang of marauders determined to get their hands on the 2nd Massachusetts’ weapons. Leading the gang is an ex-con named John Pope, who decides to use his hostages as bargaining material.
Dr. Michael Harris joins the 2nd Mass with a theory about what might save the teenagers abducted by the aliens. But the plan could be derailed when Tom starts digging for answers to questions that have haunted him since the early days of the invasion. The 2nd Mass comes face to face with skitters and mechs when they attempt to rescue Ben.
Tom and his team head out to track down more motorcycles for the 2nd Mass., relying on Pope to guide them to a good location. They hit the jackpot until they meet some skitters and harnessed teenagers at the bike shop. Back at the base, Dr. Harris and Anne disagree over the best method to gather more intelligence on the aliens.
Hal comes up with a risky new plan to rescue captured teenagers from the aliens, but it might require putting someone at risk. Meanwhile, a sudden tragedy causes Anne to make an enormous discovery that proves instrumental to Hal’s risky plan.
Lt. Terry Clayton of the 7th Mass arrives with word that the aliens are on their way to attack the 2nd Mass. Clayton’s plan to lead the children to a safe haven while the adults remain behind to fight is met with some resistance from the parents, including Tom.
Hal takes the lead fighting an unexpected threat against the children of the 2nd Mass. Anne has her hands full when Sarah goes into labor while the 2nd Mass base is being evacuated.
The 2nd Mass prepares to take the fight to the invaders with an assault on one of their bases. But Weaver’s increasingly strange behavior worries Tom that he might not be fit to command. Hal and Tom encounter a left-behind woman who employed a suspicious means of surviving the invasion, making it unclear whether they can trust her.
As the 2nd Mass. prepares for a major assault, divisions within the ranks threaten to tear the group apart. Tom has difficulty processing the profound implications of Anne’s latest discovery.
With Weaver leading several squads of fighters against the aliens, Tom remains behind to help protect the civilians as they evacuate. But a major breach in security endangers both the soldiers and the civilians. Tom is confronted with a decision that may lead him to discovering what the aliens want with the captured teenagers, humankind and the planet.
Weaver is still in command of the 2nd Mass, while Anne continues to serve as medic. They have seen many battles and are a much leaner unit now. Pope has taken command of the Berserkers, a renegade group within the 2nd Mass that Weaver doesn’t fully trust.
Tom is haunted by memories of his time with the aliens. Pope plants seeds of doubt about him among the group. Ben’s hatred for skitters grows. The 2nd Mass locate a bridge that will help them cross the river to safety ahead of an impending attack.
The 2nd Mass moves into an airport hanger. The Berserkers plan to get rid of Tom. While dealing with a loss of one of its own, the 2nd Mass receives a promise of hope from a mysterious visitor.
While on patrol together, Ben and Hal try to help a young boy and wind up having their bikes stolen. The hunt to recover them leads them to the discovery of something much bigger. Also, Matt is put in danger, and Weaver is reunited with a family member.
A familiar face returns to the 2nd Mass, but his intentions remain unknown. Meanwhile, a skitter is captured and brought back to the camp as a prisoner. And Hal bonds with Maggie as she begins to open up about her past.
Hal stumbles across bodies of de-harnessed kids and finds someone from his past. Tom and Anne grow closer. And Weaver’s health deteriorates just as Tom discovers he may have been keeping important matters from the group in order to protect them.
Ben is endangered by someone who he thought he could trust. Tom captures another hostage. Weaver offers Matt a job to lift his spirits. The 2nd Mass are trapped in a basement and face a new enemy.
The 2nd Mass pushes on to Charleston, but some are still grieving the group’s recent losses. Weaver learns more about Tector’s background before the invasion. And Matt begins to bond with a harnessed girl who was found recently.
The 2nd Mass meets new faces, while Tom comes across his former mentor, but it’s difficult to know whom to trust. Maggie realizes that Pope may not be sticking with the group very long. Tector embraces his military past.
When skitters approach the newly combined resistance force, the groups’ interaction surprises everyone. Meanwhile, Tom finds out life-changing news just as the 2nd Mass comes face-to-face with their most dangerous threat to date.
Season three of Falling Skies opens seven months after the 2nd Mass arrived in Charleston. In the interim, Tom has been elected to political office, but he has his hands full as the resistance continues to battle the alien invaders. Tom’s decision to have the rebel skitters fight alongside humans creates tension and raises suspicions that someone may be feeding secrets to the enemy. Meanwhile, Hal struggles with nightmares that seem so real, he has difficulty knowing if he’s awake or dreaming. And Tom and Anne prepare to welcome their baby.
With hostilities escalating between the resistance and the alien invaders, Tom calls on a nuclear specialist known as "The Rat King" to come up with a plan that will strip the aliens of their power. As suspicion continues to mount about a mole within the resistance, Tom and his leaders make a drastic decision that jeopardizes trust among the group. Anne, meanwhile, has a feeling that all is not right with her newborn.
The two-year anniversary of the alien invasion is fast approaching as the people of Charleston prepare for another potentially devastating offensive. A sniper attack by an unlikely gunman creates questions and doubts within the new government. Hal believes he knows the identity of the mole. And Anne’s concern for her baby continues to grow.
After the people of Charleston defeat another alien attack with the help of new advanced weaponry, Tom is invited to meet with a powerful leader. While Hal wrestles with an invasive evil, Ben struggles with his identity and the notion of being human again. And Anne uncovers startling new information that puts everyone in jeopardy.
When a mission goes terribly awry, Tom and Pope must rely on each other to survive. Meanwhile, Weaver and company search desperately for two members of the 2nd Mass who have gone missing. And Marina takes matters into her own hands in Charleston, disregarding Tom’s authority.
Hal finally reveals his internal struggle to everyone, and it doesn’t bode well for the Masons. Lourdes experiments with a risky new medical procedure. And Charleston’s government sees a massive shift in leadership when a group breaks away on a search and rescue mission.
The Masons run into trouble on the road when a family of outlaws intercepts their search-and-rescue mission. Meanwhile, looming doubts over the construction of a massive alien weapon ignite a conflict of interests. And an investigation to apprehend a killer on the loose hits a road block.
Things seem much too calm for Tom, making him suspicious of his surroundings. On his way back to Charleston, he makes a number of discoveries, some incredibly surprising and others utterly horrifying. Meanwhile, Weaver and Pope butt heads over how to handle the suspected mole.
Tom uncovers confidential intelligence about the heart of the alien operation. Meanwhile, Charleston prepares to mount an offensive against the Espheni, but a massive explosion brings the operation to a halt. And the identity of the mole is finally uncovered, but not before more blood has been shed.
When the 2nd Mass destroys a crucial Espheni base, a relentless enemy is taken down and the Mason family is reunited with those who had been lost. But the arrival of more interstellar players puts the fate of the Earth’s remaining survivors in doubt.
