Enterprise is investigating Bannon’s Nebula (on the edge of explored space), a stellar nursery that is being mined for deuterium which starships use as fuel.

The Federation outpost and refinery has had trouble getting going. The Enterprise’s engineers are here to assist.

Una arrives on the bridge to congratulate Pike on being appointed fleet captain as he is now in command of the Enterprise, the refinery, and the Farragut.

Spock notes the outpost’s proximity to Gorn space.

As the refinery is off-line, Spock and Pike think it’s a good opportunity to refuel the old fashioned way, by flying the ship through a pocket of deuterium.

As the refueling begins, Uhura picks up a strange sound on the coms. When she reports it, she’s unable to bring it up for others to hear.

She’s completing a diagnostic by recalibrating the coms in the nacelle and Pelia asks her what she’s up to. She explains that Hemmer got annoyed with her requests for recalibrations so he taught her to do it herself.

Pelia reveals that Hemmer was one of her students.

Pelia asks Uhura why she’s never spoken to her since she joined the ship. Uhura apologizes and welcomes her to the Enterprise.

Pelia leaves and Uhura continues to watch the video of Hemmer.

Pike preps Una for the refinery where she’s expected to tune-up the team.

Uhura hears the sound again as she enters a turbolift. Suddenly, a zombie Hemmer is in front of her.

M’Benga diagnoses a hallucination. He tells her she has a mild case of deuterium poisoning from working in the nacelle. He notes that she hasn’t been sleeping either and that can exacerbate the symptoms of the poisoning.

On the refinery, Pelia tries to tell Una there’s something else wrong, but Una’s sure it’ll all sort itself out.

Uhura has a hard time sleeping. She gets out of bed and discovers she’s back on Earth. She hears the sound. She’s reliving the day her parents died. Suddenly she wakes up in her bed.

James Kirk beams aboard. Sam’s there to welcome him.

They take a tour and end up sitting at the bar. Sam congratulates James on being promoted to First Officer of the Farragut. He’s the youngest First Officer in the history of Starfleet.

They debate how their father sees James’s career as the better one as he climbs the ranks quickly while Sam continues his scientific research in xenoanthropology.

Sam leaves in a snit.

At the refinery, Una’s becoming frustrated with repeated setbacks. Pelia reports that she found something while disobeying Una’s direct orders. She dismisses Una’s anger and reports they’ve found evidence of sabotage.

Chapel and Spock play chess. Spock wants to disclose their relationship to Starfleet since he outranks her and there are protocols in regards to personal relationships among crew. Chapel is concerned that letting others in on their relationship will destroy anything it might become.

Uhura interrupts them. She claims her hearing the sound is not a result of deuterium poisoning. Chapel offers to prescribe her something to help her sleep but Uhura declines it and leaves.

She sits down at the bar next to James who comments on Spock’s chess strategy. He introduces himself.

She shuts him down when he tries to engage her in conversation and leaves.

Leaving the bar, she hears the sound again. This time her hallucination is of a corridor filled with the bodies of her crewmates. Turning, she sees herself armed with a knife just before the doppelganger attacks her.

Fighting back, she punches the doppelganger and the hallucination disappears. Unfortunately, she punched James Kirk while hallucinating.

She brings him back to her quarters to fix up his nose. She explains what she’s been experiencing. He believes her and offers to help.

He takes her medical record to the doctor on the Farragut to see if it’s something they’ve seen.

Pelia brings Una and a team to a lone Starfleet officer curled into a ball and muttering to himself. When Una lays a hand on his shoulder, he becomes aware of her and identifies himself as Lt. Ramone. She asks him why he sabotaged the station and he’s confused.

While Uhura waits for James Kirk to return, she sits alone in her room and a red alert alarm goes off.

She reports to the bridge where Pike tells her they’re being attacked just before the viewscreen shatters and the entire bridge crew is sucked out into space.

Pike calls Uhura back to herself and asks why she’s at her post when she’s on medical leave. It was another hallucination.

Pike speaks with Uhura in his ready room when James Kirk joins them. He mentions Ramone and informs them that the Farragut’s medical officer had been notified the day before that he was seeing things that weren’t there.

In sickbay, M’Benga reports significant damage to the speech and language centers of Ramone’s brain. Suddenly, Uhura hears the sound just as Ramone cringes. Ramone attacks M’Benga and runs out the door.

Kirk convinces Uhura this isn’t another hallucination and insists that they stop Ramone before he hurts anyone else.

Pike and another officer track Ramone to Astrometrics where they find a dead officer.

La’an joins them. Pike and La’an follow the blood trail towards Engineering.

As Uhura and James Kirk move through the corridors, she hears the sound again and stumbles. James disappears and she becomes disoriented, falling to all fours. Then James is back and checking on her. She admits something’s wrong and she should return to sickbay.

La’an and Pike cross paths with James Kirk. They realize Ramone has eluded them. La’an is a little set back by seeing James Kirk in this timeline.

On her way back to sickbay, Uhura spots a blood drop in the corridor and bloody handprints on the hatch to the port nacelle access tunnel.

She reports her finding and follows Ramone, finding him doing something to the console. She tries to make herself understood, introducing herself and telling him about her life. He dashes for another console and activates a fuel pod ejection. He fights her and James Kirk arrives and has him and Uhura beamed out just before the nacelle explodes blasting Ramone into space.

In sickbay, Pike confers with Uhura and informs her that Starfleet gave him permission to decrypt Ramone’s personal logs since he’s deceased.

La’an finds James Kirk outside sickbay waiting for Uhura. When she comments on his compulsion to help others, he chuckles when he realizes he’s doing what his father did through James and Sam’s childhood, helping others while he neglected his family.

At the refinery, Pelia confronts Una about not liking her. Una lists Pelia’s deficiencies as an officer. Pelia accuses Una of being too used to being the smartest person in the room.

Uhura and James review Ramone’s logs in her quarters. He describes his hallucinations in frightening detail.

Uhura shares that in the time after her parents and brother died in the shuttle crash, she kept seeing their final moments whenever she closed her eyes. She believes Hemmer’s death brought those feelings up again.

Her need to repress the feelings drove her to overworking herself. She admits she doesn’t know how to face death. James points out that she needs to figure it out or let her hopes at Starfleet go.

James leaves to get them something to eat. Uhura pulls up the video of Hemmer she was watching earlier, crying at the memory. Something Hemmer says about burning out the receiver twigs for her and she realizes what’s happening to her as well as what happened to Ramone.

Finding James, she explains that her and Ramone’s brain scans show activity and damage in the same areas of the brain, the language center. She theorizes that something is trying to communicate and she and Ramone were the receivers.

They go to find Sam, the specialist in Xenoanthropology. He theorizes the lifeforms trying to communicate are extradimensional but have attached themselves to something in our universe. They don’t have a sophisticated language system so they’re using images that Uhura’s brain is interpreting as best it can. She realizes the memories and visions they’re evoking are of death and desperation.

She interprets the message as the ship and the refinery are killing the lifeform.

Sam and James hit upon the idea that the lifeforms are fused with the deuterium which the ship is consuming as fuel and the refinery is processing, unknowingly killing/torturing the lifeform.

Uhura tries to contact Pike to warn him the refinery shouldn’t be activated. He regretfully informs her the refinery was already activated.

She tells him the refinery must be shut down. He relays the message to Una and Pelia but the systems won’t respond and the refinery won’t shut down.

In the turbolift, Uhura is transported in her memories to the day of the shuttle crash. She forces herself to take a closer look. Stepping forward, the hallucination ends and she enters the bridge with James.

When Pike asks for an explanation, Uhura reports what they’ve learned all while staring directly at Zombie Hemmer. Pike says they can’t shut the refinery down. Uhura insists that they destroy it then, before it can kill more lifeforms.

The refinery is evacuated. The Enterprise and Farragut vent all the deuterium in their nacelles. The Enterprise fires its torpedoes and destroys the refinery.

Uhura’s vision of Hemmer changes to a healthy, living version. He smiles at her and nods. She confirms with Pike that it worked.

In the shuttle back to the ship, Una tells Pelia that she took Starship Maintenance 307 with her at the Academy. Pelia gave her a C. Pelia retorts that the C isn’t the issue. It’s the memory of Hemmer and Una’s resentment that Pelia took his place.

Pelia is sympathetic.

In the bar, James and Uhura have a drink. She shows him some pictures of her family. Sam stops by and comments he’ll probably write a paper on the lifeforms they’ve discovered. Sam fishes for an apology from James but it goes unrequited and Sam storms off.

Spock stops by to comment on how frustrating he finds Sam. Uhura makes introductions. James invites Spock to sit with them and the three of them have an evening of it.