It is morning, and Marco is in bed asleep, but is woken up by the puppies. He tries to get away from them, but they want him to take them for a walk in the park. Unfortunately, the weather outside is overcast with heavy rainfall and flooding. So decides to go and ask Star if he can borrow her Dimensional Scissors. Marco finds Star practicing with her wand using a tennis ball for spell-targeting. She gives Marco her Dimensional Scissors, and he uses them to cut open a dimensional portal to the park, allowing the puppies to have their walk. Realizing the potential usage of the dimensional scissors, Marco starts using them for everything, including getting snacks from the refrigerator, getting drive-thru takeouts, and going to the beach all from the comforts of his bed. However, he abuses the scissors too much that the next portal he opens turns out different than the rest. Then someone from the portal suddenly pulls him into another dimension and seizes the scissors.
In the new dimension, Marco encounters Hekapoo, the Scissors Enforcer and one of the members of the Magic High Commission. She asks Marco where he got the Scissors from, and he says he borrowed them from Star Butterfly. Hekapoo does not believe him since she is the forger of all dimensional scissors and Star's scissors originally belong to her. Wanting to return the scissors to Star, Marco wishes to rightfully earn them from Hekapoo. At first she laughs, but after seeing that he is pretty determined, she gives him a challenge: she will give him the scissors if he can blow out the flame floating above her head. However, Marco's attempt to blow out Hekapoo's flames proves to be difficult at first due to her quick speed. He tries to outsmart her, but she sends him through another portal. Upon entering another dimension, Marco goes over a cliff, but succeeds in outwitting Hekapoo and blowing out her flame before falling. Unfortunately, that Hekapoo was a fake, and Marco finds himself facing hundreds of Hekapoo duplicates. The real Hekapoo opens multiple dimensional portals, and she and her duplicates scatter into many different dimensions. She tells Marco that it could take him years to find her and offers him a way back home, but Marco is determined to get the scissors back no matter how long it takes.
Meanwhile, Star is still doing her target practice until when a man walking a dog in her room, having entered through one of the many dimensional portals that Marco left open in his bedroom. After retrieving the laser puppies, Star discovers Hekapoo's portal and calls Pony Head. She recognizes the portal, and reveals that she stole the dimensional scissors she gave to Star from Hekapoo without earning them. Suspecting that Hekapoo took Marco, Pony Head suspects that he his dead by now. Regardless, Star heads through the portal to save him. Back in Hekapoo's dimension, sixteen years have passed, and Marco, now grown up and hardened from the years of fighting and surviving in the wild, has tracked down Hekapoo and her remaining duplicates to her scissors forge. After blowing out the two duplicates standing watch outside the forge, Marco confronts Hekapoo, having blown out the flames of all her duplicates. She allows him to blow out her flame without resistance, and for finally completing his challenge she rewards Marco with his own pair of dimensional scissors. Suddenly, Star bursts in and commands Hekapoo to release Marco. Marco reunites with Star, and after a brief moment of infatuation with his new look, Star reveals that while he has spent sixteen years in this dimension, only eight minutes have passed on Earth.
Since Marco has not missed anything, Star tells him to use his new scissors to take them home, but Marco has grown too comfortable in his new life as a warrior. However, when Star reminds him of his friends and family, he has a change of heart and returns home with Star, leaving his Dragon cycle, "Nachos", in Hekapoo's care. Upon returning to Earth, Marco's body has reverted to that of a teenager, meaning he and Star can still go on adventures together. As Star leaves to make some nachos, Marco tries to settle back into his old life; having been away for sixteen chronological years.
- Eden Sher as Star Butterfly
- Adam McArthur as Marco Diaz
- Zosia Mamet as Hekapoo
- Jenny Slate as Pony Head
- Adam McArthur, who provides the voice for Marco Diaz, tweeted about "Running with Scissors" on January 9, 2017, calling it "one of my favorite eps I've ever recorded".
- He also admitted that had to audition to voice adult Marco.
- "Weird Al" Yankovic also had a famous song album titled "Running with Scissors" that was released in 1999.