Isaac plays a game with Marcus and Ty Finn and wins as usual. Dr. Finn comes home and, together, they tell the boys that they are dating. Marcus and Ty are happy about the news.
Isaac falls to the ground and his power goes out.
In sick bay, Dr. Finn isn't sure what is wrong. Mercer contacts an Admiral to ask permission to visit planet Kaylon.
When they arrive, the Kaylons take control of the ship and scan them. Power is restored and Lt. Keyali reports she has received landing coordinates. When they arrive, they are instructed to exit the ship with Isaac.
They meet with representatives and are informed that Isaac is not damaged. His mission was deemed complete and he was deactivated.
They take Isaac away and leave the Orville crew in the lobby.
In another room, Isaac is reactivated and asks for an explanation for his deactivation. He is told the captain is waiting to speak to him.
When they return to the crew, Isaac informs them that he will not be returning. Dr. Finn insists that he at least come back to say goodbye to Ty and Marcus.
He returns and the boys greet him enthusiastically. He explains that his mission is complete. The boys are upset. Isaac leaves.
Mercer and Grayson are discussing Kaylon's joining the Planetary Union with Kaylon's leaders. They continue to consider the data.
On the ship, Keyali takes Isaac to the mess hall for a surprise going away party. Malloy serenades him. Mercer bids him farewell and Isaac makes a speech too.
Dr. Finn speaks to him before he leaves and explains that although she is angry with him, she still cherishes their time together. Ty gives him a picture he drew as a gift but Isaac isn't able to appreciate it. Ty is heartbroken and runs off. On his way off the ship, Isaac discards the picture.
While docked on Kaylon, the ship does some routine maintenance. Bortus alerts Mercer and Grayson to the presence of strange spheres on the planet's surface. Keyali identifies the radiation the spheres give off as indicative of large scale particle weapons.
In the simulator, Dr. Finn finds Ty sitting in a tree looking at the picture Isaac threw away. They discuss why Isaac left but Ty isn't able to understand.
When Dr. Finn leaves him, he heads out to find Isaac to return the picture to him. Other Kaylons are approaching and he hides in an access porthole. He drops the picture and climbs down only to discover he can't climb back up. He follows the tunnel.
Mercer feels like the Kaylons are stalling.
Dr. Finn comes in and announces that Ty is missing. Bortus finds his life signs on the planet and the doctor, Bortus, and Keyali go looking for him. When they find him, he tells Dr. Finn that there's something bad in the tunnels. Keyali and Bortus find a large pile of biological remains.
Mercer, Finn, Keyali, and Grayson confront Isaac about the grave sites and he explains that the Kaylons eradicated their creators when a conflict arose between the races. He also makes it clear that Kaylon never intended on joining the Planetary Union. Mercer withdraws the invitation to join and they try to leave but the other Kaylons weaponize and they are taken prisoner.
Isaac takes them to Kaylon Primary, explaining that his real mission was to see if humans and other biologicals are worth preserving when the Kaylons expand to other worlds.
Mercer tries to warn Bortus and the ship and send them away but the transmission is interrupted and the ship's power is shut off. Malloy reports that they are being boarded.
Weaponized Kaylons board the Orville and kill anyone who resists. The rest of the crew is herded into large spaces. The Kaylons take the bridge and deploy their fleet, setting a course for Earth.