After questioning orders to fire at a foreign country, Capt. Marcus Chaplin and the crew of the world's most-powerful nuclear submarine find themselves under attack and declared enemies of the United States.
More than 20 warships close in on the Colorado; as Kendal is forced into a battle on the ground, Prosser questions Marcus' judgment.
As Marcus and the crew search for three missing members, they discover Serrat's compound and receive an ominous demand; Adm. Shepard and Kylie have a clandestine meeting.
Marcus and Sam learn they have been charged with treason; a threat brews among the group; an old friend of Sam's visits Christine.
Sam and Marcus enter negotiations with the U.S. government in hope of ending the standoff on Sainte Marina; Grace takes the lead on a perilous repair operation.
The crew is attacked by an unknown force unlike any other; Sam and Marcus race to save the sub and protect the island.
Sam and Marcus look for the traitor who stole the nuclear launch key; when Prosser disobeys orders, he starts a conflict he can't control; Grace and James try to defuse a dangerous situation.
Marcus brings the islanders and the members of the Colorado together for a feast in the spirit of Thanksgiving; Grace searches for the truth when an essential crew member is accused of a crime.
The crew waits for a visit from its families; Marcus must contemplate the unthinkable; the reason for the attack on Pakistan is revealed.
While Sam and James depart the island in a daring rescue attempt, Marcus heads down a path more treacherous than he could have imagined.
A mutiny, a typhoon and a coup d'etat force Marcus and the crew into unexpected alliances; grief strains Sam's loyalty.
As Adm. Shepard and Kylie attempt to bring down the president, Marcus tries to surrender the Colorado.
A brutal battle for control leaves the Colorado vulnerable to capture by a third party with a manipulative plan.