An otherworldly encounter puts Tree Trunks on the trail of a conspiracy in the Candy Kingdom. 
On a starry night, an unidentified flying object (UFO) can be seen rotating in the sky, high above Tree Trunks' and Mr. Pig's house. In the house, everyone is sound asleep. Mr. Pig briefly rouses from Tree Trunks' loud snoring and goes back to sleep. A moment later, a large glowing screen of blue light appears at Tree Trunks' bedside. A creature that is visibly extraterrestrial emerges from the light and soundlessly wakes Tree Trunks up. She expresses delight upon seeing the alien, who takes her into the light with him.
When they arrive at the other side, more aliens can be seen moving about in a peach-coloured universe that has mushrooms growing around it. The aliens embrace Tree Trunks, who seems to know them all. A curtain is drawn to reveal five alien-elephant hybrid children and a leotard-clad grasshopper creature behind it, whom Tree Trunks refers to as her babies. Her voice comes out deeper and in slow-motion in this universe.
Back in Ooo, Mr. Pig awakens again to find his wife missing from bed, and pads around the house in search of her. He hears Tree Trunks saying goodbye to someone back in their bedroom, and returns to ask where she had gone, to which she honestly tells him she was visited by aliens who brought her to see her hybrid children. Mr. Pig simply laughs, probably thinking she had been dreaming. They discuss going to Princess Bubblegum's fireworks show the following day, which Tree Trunks initially refuses to go due to her distaste for the Princess, but eventually agrees to accompany Mr. Pig.
At the fireworks show the next day, Princess Bubblegum plays a short piece of electronic music (ending in "Science rules!") for the crowd, before bringing their attention to some graphs and equations on her chalkboard. She whispers, "I'm doing the right thing," though she appears uncertain, and proceeds to set off a rocket that resembles her countenance into the sky.
Seconds after it flies into space, Tree Trunks is abducted by aliens, who point out the rocket that has crashed into their realm. The rocket head opens to let out streams of candy matter, which begin to invade and attach themselves to the aliens' bodies. Tree Trunks is transported back to Ooo, and she immediately berates Princess Bubblegum for hurting the aliens. Princess Bubblegum is surprised that Tree Trunks knows the rocket went into space, but insists she does not know what she's talking about.
Tree Trunks does not let the matter rest, going out on the Candy Kingdom streets to protest against the Princess and her "secret space war". Most of the candy people think she is just another lunatic, but Starchy invites her to join his conspiracy team, the Veritas Brigade. She is eager to fight against Princess Bubblegum and agrees to join them, spearheading an infiltration into the Princess' space programme facility that very night.
When Tree Trunks breaks into the facility with the help of the Brigade, she is shocked by the number of Princess Bubblegum-like rockets inside, all of them much bigger than the first one that was launched. Tree Trunks is certain the Princess is planning a full-scale galactic invasion and starts trying to dismantle the rockets. Upon opening one of the rockets, she sees a flurry of candy matter inside it and gets ready to extinguish them. Just then, a livid Princess Bubblegum and her Banana Guards burst in and stop her. Before she can be captured, Tree Trunks is abducted right before their very eyes.
Tree Trunks finds herself back in the alien universe, where most of the aliens have been infected by candy matter. She quickly hits one of the mushrooms, which proves to be a kind of teleportation device, and abducts Princess Bubblegum from Ooo. When the Princess arrives in the alien universe, she is confused and asks Tree Trunks where they are. Tree Trunks tells her, "You already know." Looking around her, Princess Bubblegum realises that the candy matter she had released into space are taking over the indigenous life forms in the alien universe. She is horrified, and decides to foregather all the candy matter back into the rocket. Everything goes white.
At dawn, Princess Bubblegum and Tree Trunks wake up in the middle of a rural grassland. Princess Bubblegum is still dumbfounded by the experience. On their way back to the Candy Kingdom, the Princess apologises to Tree Trunks for what she did to the aliens, as she never meant to hurt anyone with her space programme. It had meant to be a way to seed new Candy Kingdoms on uninhabited planets, in case Ooo is one day destroyed. Tree Trunks looks up at the UFO in the distant sky for a moment and decides to help the Princess find a space for her programme. Though the two of them will never be friends, Tree Trunks respects her as a mother and as a fellow believer of the infinite promise of the cosmos above.
That night, Tree Trunks is visited by an alien again. He speaks this time, apparently having learnt English from the Internet, and tells Tree Trunks that his people will fly Princess Bubblegum's rocket to their old uninhabited planet so they can have space to build their new kingdom. However, as the galaxy is so far away, he will not be able to see Tree Trunks again for another 40 years. When Mr. Pig wakes up beside her and demands to know who the alien is, Tree Trunks finally introduces her two husbands.
- Tree Trunks
- Princess Bubblegum
- Candy Probes
- Tree Trunks' Alien Husband
- Tree Trunks' Alien Children
- Mr. Pig
- Candy People
- Finn (cameo)
- Jake (cameo)
- BMO (cameo)
- Sweet P. (cameo)
- Interestingly, each of Bubblegum's rockets sports a different style of "clothing," representative of the different clothing Bubblegum has worn throughout the series.
- Princess Bubblegum's small device is in the shape of the state of Texas.
- There is a population graph on Bubblegum's chalkboard that appears to show population from the year 10,000 BC to the year 4000 at least. The huge drop in population around the 21st century is probably a result of the mushroom war. In a farther out shot of the graph from a few seconds before, there's a huge growth in population forecast around 4000 BC, where the population level returns to around modern levels.
- The aliens that visit Tree Trunks are Grey Aliens, the most common depiction of aliens in pop culture, with grey skin, large black eyes, and large heads.
- The Banana Guard channeling "Booshy" may be a reference to YouTube channeler Darryl Anka and his channeling of an interdimensional being known as "Bashar." Similar facial distortions are seen in channeling both Booshy and Bashar, as well as similar hand positioning and a drastic change in vocal tone.
- The aliens (and somewhat the plot of the episode) are similar to the visitors from the pilot episode of South Park.
- The control unit being in the shape of Texas could be a reference to NASA's mission control being in Houston, Texas.
- The candy matter from the rockets may be the little creatures PB was working on in "The Lich."
- In the episode "Apple Wedding," when Treetrunks and the wedding guests get sent to the dungeon by Princess Bubblegum, telepathic waves beam into Treetrunk's head and her eyes dilate as she announces, "The elephant graveyard is calling me now. Okay, hold your horses, I'm comin'." This might have been the aliens communicating with Treetrunks.
- Princess Bubblegum is increasingly worried that the Candy Kingdom will be destroyed, one way or another, so she has been sending seed-rockets of candy-life into outer space, hoping that they will land on inhabitable planets to start new Candy Kingdoms. The flash-forward in "Lemonhope Part 2" to 1,000 years from the present time showed that the Candy Kingdom was abandoned by that point in time (the storyboards point out that it was "abandoned" not "destroyed"), possibly meaning Bubblegum's space mission was eventually successful.
- The resistance movement that Tree Trunks joins criticizes Princess Bubblegum as a fascist - keeping with the running subplot that her rule can seem uncomfortably tyrannical, but she feels she is doing what she must to shepherd and protect the kingdom. When she was briefly ousted as Princess, the kingdom was nearly destroyed, and only restored to stability when she basically seized power as an anti-democratic monarch again.
This episode was censored in some countries. See Censorship of Adventure Time for more information.