With their mission now fully dedicated to spreading the cure, Nathan James puts a call out to civilians to meet at pre-selected ports across the country, where all will receive the cure. However, small Immune factions remain active in their quest to fight the cure and fulfill Ramsey's dreams. Will Nathan James regain America's trust? Has the havoc and destruction caused by the Immunes ended all hope to spread the cure? Or will Nathan James prevail against the enemy and finally spread the cure?.

After retrieving the mastermind behind the Immune communications network, Nathan James finds itself trapped between the sub and civilian blockades set up by the Immunes. Chandler sends Dr. Scott and the cure off the ship under the protection of XO Slattery as the James heads towards its inevitable final showdown with the sub.

Sean Ramsey broadcasts a message implicating the Navy in a devastating disaster. It's now more important than ever for Chandler to infiltrate their network and regain the trust of the American people. Nathan James locates the source of the Immune's signal - a mysterious oil platform in the middle of the ocean. Once there, Chandler and his team engage in a brutal battle with civilian forces who have aligned themselves with the Ramsey's plan.

Rachel is hard at work on a new, more efficient version of the cure while Alisha decodes a message found on a cell phone recovered from the Immunes on land. A suspicious death on the ship forces Chandler to launch a murder investigation, causing dissent among the crew and threatening to upset good order and discipline. Armed with new information provided by Michener, Nathan James heads to New Orleans, only to find that the Immunes have a terrifying surprise in store for them there.

With Dr. Scott on the verge of a breakthrough, Chandler and his team set out to land in search of much needed supplies and materials for her lab. Once there, Burk stumbles upon a gang of children who have been offered a bounty by the Immunes for information on the U.S. Navy. A vicious battle ensues when the Immunes come to collect their prisoners. Back on the ship, Rachel's efforts to produce a spreadable cure depend on Niels - her success now inextricably linked to the scientist who nearly erased mankind.

While trying to piece together Dr. Hunter's lost formula, Rachel deals with the fact that her sworn enemy is on board the ship; Chandler tries to reverse the brainwashing Michener suffered at the hands of the Ramseys.

Slattery struggles to evade the sub; Chandler and the land team infiltrate the immune compound; Danny discovers that Niels is working for the Ramseys; Chandler manages to encroach Sean's inner circle.

Chandler tracks the immunes to Northern Florida; Rachel comes across a secret formula that her mentor was working on; Chandler's team locates an immune compound.

With a small group of survivors from Solace in tow, Chandler and his crew square off against an enemy of the most dangerous kind - a nuclear-powered submarine led by rogue British naval officers, Sean and Ned Ramsey. XO Slattery interrogates a captured mercenary from the hospital ship in an effort to extract information on the sub and its mission. As Nathan James engages in a perilous game of cat-and- mouse, the truth about the mercenary sub unfolds.

The crew of Nathan James discovers that hospital ship USNS Solace was sent to sea to wait for Dr. Scott's cure. Captain Chandler sees an opportunity to add another ship to their fleet while Rachel is eager to find a lab better equipped to replicate the vaccine. When Solace fails to respond to radio communications, Chandler and his team board the ship..and come face-to-face with an unexpected enemy.

Nathan James returns home to Norfolk on a mission to produce and mass distribute the cure. With his family now safely aboard the James, Chandler sends his crew in search of their own friends and loved ones. Who, if any, will find their families? And will those who do return to the ship?.

Rachel tries to help the sick while remaining a prisoner; Slattery and the crew try to regain control of their ship.

After the horrifying revelations and reversals of fortune in Baltimore, Chandler and his fractured team join forces with an underground resistance in an attempt to defeat Amy Granderson. With doses of the cure running low, Rachel tries to do some good for the sick while remaining a prisoner at Avocet. Meanwhile, Slattery and the crew of Nathan James are in a race against time to save an injured Dr. Tophet and regain control of their ship.