Plot

With monkeys for testing, they work towards a vaccine but with no cure in sight, a serious lack of monkeys and increasingly depressing distress calls, they think about returning to Nicaragua.

Captain Chandler tells the crew the cure is within reach, but monkey test have only begun and the first batches of six all die, proving a vaccine may actually take long to make. When Danny suddenly collapses with symptoms like the plague's, panic spreads, which Quincy feeds in the hope the CO will liberate him. CO and XO must now regain the crew's trust to avoid desertion, which would be legal as service contracts are running off.—KGF Vissers

With the team back from their eventful trip to get Dr. Scott her test monkeys, the guys aren't talking about what they saw, or their encounter with the jungle kingpin El Toro.

In CIC, a sailor tells Granderson that the crew is starting to ask questions about what they hear on the radio distress signals.

Jeter, Chandler, and Slattery try to figure out what to tell the crew about El Toro. They came back covered in blood and the crew has questions. Jeter and Slattery argue they shouldn't give details about the mission, so that the crew will still have hope.

Meanwhile, Chandler visits Dr. Scott, who explains she has to find the right combination to get the vaccine to work.

Chandler goes on the bridge to address the crew over the intercom. He tells them they encountered a kingpin enslaving people and were able to help them, but there were others they weren't able to help. Dr. Scott has 34 monkeys and they're heading home - he thinks she'll have a vaccine by the time they get there.

Later, Dr. Scott has a crisis as those test monkeys die and consults with Commander Tom Chandler. All six of the ones she tested on died and she has no idea why. He advises her to drop them into the ocean at night and tell no one.

The next day, Chandler briefs XO Mike Slattery and CMC Jeter. She's going through her test monkeys quickly. Chandler doesn't want to burn more fuel heading for home if they're just going to have to turn around again for more monkeys.

Quincy Tophet plays chess with Bacon and suggests the fact the boat has stopped means that something must be seriously wrong with Dr. Scott's experiments. He tells Bacon that Chandler is hiding something from him.

At night, Dr. Scott dumps the monkeys bodies overboard. Two sailors, Cossetti and O'Connor, on watch see her.

Six more monkeys died, more quickly than the first batch. Slattery wonders if they should involve Quincy but the captain objects.

In the rec room, the crew starts speculating on the away team's health, thinking that they're sick. Tex assures them they were tested when they returned and are fine. But then Danny Green stumbles in, looking feverish and passes out.

O'Connor sees him and begins to get seriously worried.

Dr. Scott goes to check on Lt. Green, assuring him that he doesn't have the virus, even when he coughs up blood. She thinks it's most likely he got something from an insect bite.

Doc Rios comes to check on him wearing full protective gear, which everyone he passes in the hallway sees him in.

Dr. Scott tries to convince everyone to calm down, but Chandler wonders if Danny could have a mutated strain. Dr. Scott assures him she tested for the core virus and is positive she would have detected it. She says the mistakes she made with the vaccine are different, and part of experimenting.

Nevertheless, Chandler calls Slattery to lockdown the ship. Everyone stays where they are and puts on suits as the ship is sealed off.

Everyone but Kara -- who races to the rec room to be with Danny, announcing to Chandler that they were together and if Danny is sick, so is she.

Doc Rios tests Danny's blood to determine what he has.

In the rec room, Birk asks Dr. Scott about the "mistakes" she made with the vaccine. But they're interrupted when Rios calls. Danny has dengue fever, for which he needs fluids and Tylenol. It's not contagious.

Chandler dismisses everyone and talks to Kara alone as Slattery announces that there is no threat.

Chandler asks Kara what happened the night they took the RIB to the Russian ship and were late. She tells him about Danny slowing down to try to convince her to get off. Chandler points out she just potentially exposed everyone running through the ship to get to Danny. He reminds her of her oath and duty to her shipmates.

Out in the hallway, Dr. Scott essentially tells Chandler he should have trusted her. He reminds her that he's killed for her, delayed going back to his family for her and any number of things -- but she says it wasn't for her, it was for the human race, and he needs to find a way to trust her again.

Bacon checks in with Quincy about a scheme to leave the ship.

Chandler reviews Dr. Scott's record.

Miller talks to O'Connor and Cossetti, they try to convince him to leave the ship with them. They're all summoned to a briefing from Chandler.

He acknowledges he's made some mistakes in the past few days in keeping information from them. He reminds them the mission isn't about the crew, it's about everyone else left. Chandler plays recordings of people asking for help over the radio.

Then he opens the bay doors to reveal Dr. Scott working in her lab and invites everyone to look. He tells them Dr. Scott has dedicated her life to working on vaccines, and she fought to be on this case. He asks her to explain what's happening.

She addresses the crew, telling them right now her vaccine is failing in the monkeys, but she'll keep at it. Chandler tells the crew they have to believe in each other not just when they're succeeding, but when they're failing. Chandler acknowledges the group planning to leave, and says he knows their enlistments are up, so he'll give them a RIB and supplies for their back pay and they can leave tomorrow morning at 7am.

Chandler worries that if the group of 16 goes, hope goes with them.

The next morning, Chandler, Jeter and Slattery find the group of 16 waiting. Cossetti presents Chandler with a flag and announces they want to re-enlist.

Chandler leads them through the oath.

Later, he goes to check on Danny Green and finds Kara Foster there with him. They agree on punishment for her and he asks her to train some junior officers in CIC. He also wants her to explain to others why her behavior is so dangerous.

Chandler drops in on Quincy, telling him to quit talking to Bacon. He takes his chess board.