More than 20 warships close in on the Colorado; as Kendal is forced into a battle on the ground, Prosser questions Marcus' judgement

Aa search for three missing crew members leads to Serrat's compound and an ominous demand. A clandestine meeting between Kylie and Admiral Shepard confirms that the fire order came through a back channel.

Marcus and Sam learn they have been charged with treason; a threat brews among the group; an old friend of Sam's visits Christine.

In an attempt to end the standoff on Sainte Marina, Marcus and Sam enter into tense negotiations with the U.S. Government. Meanwhile, when a critical system fails, Grace must take command of the Colorado 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.

Sam and James depart the island in a daring rescue attempt. Back on the island of Sainte Marina, a Chinese diplomat arrives to make a deal with Marcus. With scarcity and a prison problem plaguing him, Marcus finds himself treading down a more treacherous path than he could have imagined.

A typhoon, a mutiny and a Washington coup d'etat will force Marcus and his crew into unlikely alliances. As Sam's grief strains his loyalty to Marcus, will Sainte Marina get the supplies it so desperately needs? How far will Marcus go to ensure the crew's survival -- will it cost him his life?

Kylie works with Admiral Shepard to bring down the President, using evidence of what really happened in Pakistan.

A brutal battle for control leaves the Colorado vulnerable to capture by a third party with a manipulative plan.