Karaoke night on board the Orville sees Bortus about to perform "My Heart Will Go On" from Titanic when the festivities are interrupted by a message from Admiral Halsey.
Grayson and Mercer take the Admiral's call regarding the Navarian/Bruidian conflict over the planet Lapovius. They are sent to pick up a forensic archeologist from the U.S.S. Olympia who will determine which species has the better claim to the planet.
Since the species loathe each other, Kitan finds quarters for them on different decks on opposite sides of the ship. The archeologist is sent from the Olympia by shuttle and when Kitan realizes who he is, she tries to stop it. The archeologist is Darulio, the blue-skinned alien who Grayson cheated on Mercer with. Kitan escorts him to his Science Lab and quarters. En route, Darulio trips over Yaphit.
In sick bay, Clyden and Bortus are having Dr. Finn give Topa his shots. Clyden is upset that Bortus will be working late and Bortus confides in Dr. Finn that they are having a difficult time adjusting to parenthood. Yaphit enters sick bay with flowers and a guitar and asks Dr. Finn out again. She tells him off and threatens to submit a formal complaint if he pursues her again. He leaves.
Grayson has an awkward conversation with Darulio, explaining that she is working on rebuilding a professional relationship with Mercer. He reaches out to brush a stray hair off her face and she starts to admire how healthy he's looking. They begin to confide in each other about the importance of "me time".
The Bruidian and Navarian representatives board The Orville but Grayson isn't in the shuttle bay to greet them. Isaac locates her in her quarters and Mercer goes down there and finds her in bed with Darulio in a complete replay of the day he found them together when they were married.
When they get to the shuttle bay, the Bruidian and Navarian delegations are arguing. Kitan has to disarm one of them when he draws his weapon. Mercer manages to appease both and convince them to come together the next day to discuss possibly finding a peaceful compromise.
Grayson and Kitan discuss the situation with Darulio and how Grayson went from having a sensible conversation with him to jumping in bed with him again. Grayson thinks that she might be in love with Darulio.
Mercer and Malloy discuss the situation and Mercer decides to fire Darulio. When he tells him, Darulio tells him that he's about thirty-six hours away from identifying the DNA he found inside the artifact he was hired to examine. Mercer retracts the firing and then asks Darulio out for a drink.
Dr. Finn shows up at Yaphit's quarters all dressed up and asks to come in. She looks around and then asks him to kiss her. It's incredibly weird.
Malloy meets Mercer in his quarters where Mercer is getting ready for his date with Darulio. Malloy is confused by Mercer's sudden about-face on the Darulio issue when he should be brokering the peace talks.
Kitan and LaMarr are discussing Grayson's strange behaviour when the Navarian delegation arrives in the mess hall wondering about the artifact results and why both the captain and the first officer are ignoring them. Kitan tries to calm him down when Mercer arrives, excited to see Darulio. He brushes off the Navarian concerns and rushes to Darulio's table only to find Grayson there already.
Grayson realizes Mercer's interest in Darulio and tries to warn him off.
The Bruidians contact Bortus on the bridge and demand to speak to the captain as they feel the Navarians are influencing the artifact testing. When Bortus asks the bridge crew where Mercer and Grayson are, Kitan and Malloy report that they are both acting strange and heavily interested in Darulio.
Dr. Finn's sons come onto the bridge and tell Kitan that Dr. Finn has been locked in her office for hours and won't answer. Kitan goes down to sick bay to investigate and finds Dr. Finn having intercourse with Yaphit in a manner of speaking.
When Kitan questions her, Dr. Finn insists that she and Yaphit are soul mates and are in love. Kitan orders Yaphit back to his quarters and to have no further contact with Dr. Finn until she figures out what's affecting the crew.
Bortus contacts Kitan and informs her that the Navarians and Bruidians are about to give up on any settlement and fight it out instead.
In the Science Lab, Grayson is hanging on Darulio's every move and Mercer arrives with a picnic basket to share with Darulio. Kitan interrupts their vying for Darulio's attention and sends them off to deal with the delegates so she can speak with Darulio.
Under Kitan's interrogation, Darulio admits that his pheromones are affecting Mercer and Grayson and they probably transferred to Yaphit when he tripped on him. Kitan escorts him to sick bay to have the pheromone analyzed.
Grayson and Mercer meet with the delegates who are on the brink of violence. Mercer is too wrapped up in his new-found love of Darulio to care and the delegates summon their respective fleets.
When the fleets arrive, Mercer is incommunicado in his quarters with Darulio and Grayson is refusing to respond as she cries her broken heart out in her quarters. Darulio sees the two fleets about to go to war and realizes that his pheromones will cause thousands of deaths.
Bortus orders the delegates to command their fleets to stand down but they refuse. Kitan confines them to quarters without communication devices. Isaac suggests extending the deflector to create a barrier between the fleets but Chief Newton says he needs Yaphit to configure the conduits. Darulio arrives on the bridge with a plan.
Yaphit runs into Dr. Finn on the way to Engineering and she's armed and distraught that he hasn't replied to her messages.
The battle begins and the deflector plan is wasted because Yaphit never made it to Engineering. Kitan brings the delegates onto the bridge, holding hands with each other, and opens a channel to both fleets. The ambassadors send their respective fleets home and then kiss as they are planning to get married. This came about through a "suped-up version" of Darulio's pheromone introduced to the Bruidian sweat glands.
Mercer is cleared for duty by Dr. Finn who is also weirded out by her experience. Mercer and Grayson apologize to each other and Darulio arrives to announce that the results on the artifact reveal that the DNA is both Bruidian and Navarian so they will have to share the planet as both species have a legitimate claim to the planet.
Before he leaves for his shuttle, Grayson asks if he was in heat when they slept together the first time and he admits he might've been.