The students of Jefferson County Middle School are going on a field trip to the Museum of Natural History. Milo, Zack, and Melissa's subway car gets derailed on their way to their trip. While trying to find their way to the museum, they encounter a society of construction workers who have been underground for a long time.
Milo, Melissa, Zack, and their classmates from Jefferson County Middle School enter a subway station in order to travel to the Natural History Museum. While en route, however, the car that the three enter becomes detached from the rest of the train and ends up going down the wrong track. Surviving the mishap, the trio encounter the Undergrounders, a group of construction workers who have been trapped in the underbelly of the city for about a month. The group have formed their own society of Subterranis, where they live among various leavings of surface civilization and eat rats.
At the museum, the teacher is agonizing over the absence of Milo and the others while Bradley Nicholson revels in the fact that Milo's absence is allowing him to be the center of attention, though he fears it cannot last. Back underground, the trio and the Undergrounders are found by Diogee, whom Milo realizes can lead the group home due to his uncanny sense of direction. They then follow the dog only for Milo and Melissa to become trapped in a cave-in, forcing Zack to go to their rescue. Diogee then leads the group to an abandoned subway car that takes them into the museum, reuniting Milo and his friends with their classmates. Most of the Undergrounders then leave to return to their normal lives, though Scott opts to return to the underground.
For a full transcript of "The Undergrounders", click here.
The image gallery for "The Undergrounders" may be viewed here.
On September 19, 2016, the episode became available for free streaming on iTunes and Amazon.
On September 26, 2016, the episode became available to watch early on the Disney XD App and Video On Demand.
October 17, 2016 (Canada)
December 31, 2016 (Latin America; Sneak Premiere)
January 10, 2017 (Spain)
January 28, 2017 (Latin America; Official)
February 10, 2017 (Southeast Asia)
February 13, 2017 (Japan)
February 16, 2017 (Germany)
A promotional video for Milo Murphy's Law showed Vinnie Dakota and Balthazar Cavendish appearing in the background while Milo gets stuck at the turnstile at the subway. They disappeared during the aired episode, but oddly the pistachio cart remains.
The theme Milo plays on his accordion was previously used in the Phineas and Ferb episode, "Run Away Runway" to introduce Gaston Le Monde.
When Mort is seen carrying a bunch of pink quartz, a small note on the box says "Rose Quartz"; a possible tip of the hat to a character from the popular Cartoon Network series Steven Universe. However, it could just be referring to the actual mineral.
One of the statues in the Undergrounders civilization resembles the Statue of Liberty.
Dani Vetere's name is misspelled as Dani Veteri.
When Mort grabs rose quartz from the box, the quantity inside it doesn't change.