The Ultra Guardians are summoned by Lusamine, and Wicke explains that they detected strong magnetic reactions at the center of Wela Volcano Park on Akala Island. She adds that the force is quickly spreading and is interfering with the Aether Foundation's ability to detect Ultra Aura. The Ultra Guardians accept the mission and fly over to Wela Volcano. There, Lillie and Sophocles take out sensors, and the Ultra Guardians split up into two groups: the boys (Ash, Kiawe, and Sophocles) investigate the mines; while the girls (Lana, Lillie, and Mallow) decide to scour the surface.
The boys soon get a signal, and they discover a group of Alolan Geodude and Graveler. Sophocles points his sensor at the wild Pokémon, which detects a massive magnetic force. Rotom affirms that the dual Rock- and Electric-types radiate strong magnetism. Pikachu rushes over to the Geodude and Graveler and returns to Ash with a mysterious golden stone. Kiawe quickly confirms that the object is actually a Spark Stone, a magma-hardened and electricity-infused rock that is also Graveler and Geodude's favorite food. Kiawe clarifies that he hasn't seen this type of behavior before, and normally Geodude and Graveler live underground.
Suddenly, a male Trainer arrives and calls out his Pinsir to scare off the Graveler and Geodude. Another man appears, and with a pickax, he finds a large amount of Spark Stones. Kiawe decides to confront the men, but they dismiss his concerns and claim the Spark Stones are available to everyone. The situation quickly escalates into a battle, as Pinsir approaches using Thrash. However, Marowak gets in first and defeats Pinsir with one Flare Blitz. The men then flee into the mines, with Sophocles, Kiawe, and Ash in pursuit.
Inside the mine, they soon locate another two men who are in the middle of mining for Spark Stones. Ash, Kiawe and Sophocles look on in shock when suddenly the trio of Hikers from earlier appear behind them. The Hikers explain that the rock hunters are interested in making a profit from the Spark Stones, which can be turned into expensive jewelry. Kiawe is burning with intense anger, so the trio decide to continue their search for the rock hunters. They soon arrive at a dead end, but they can hear noises on the other side. Sophocles's Metang makes quick work of the obstacle and the boys enter into a well-lit cavern. However, the intensity of the heat overwhelms Rotom and the group spot the guys and Pinsir from earlier lying unconscious on the rock floor. The boys manage to wake up the two rock hunters who go on to explain that they were attacked by a boom and zap. Ash and his friends are unable to figure out what the pair means, but soon the odd sound occurs again and causes a rock to fall. Kiawe has his Marowak use Bonemerang to successfully deflect the debris.
A group of angry Geodude and Graveler appear, and their leader, a Golem goes onto unleash another attack as the two rock hunters flee the chaos. Ash and his friends are also forced to run as Golem continues to attack. Marowak later attempts to intervene, but is struck down by the explosive force of Golem's move. With Marowak severely injured, Ash and Sophocles send out Pikachu and Togedemaru to confront the rampaging horde. Pikachu goes in for an Iron Tail and Togedemaru attempts a Zing Zap. Unexpectedly, Golem picks up one of the Geodude and launches it directly at Pikachu and Togedemaru. Golem is spurred into a maniacal mood and begins shooting more Geodude at the mine walls. Golem then turns its attention to Ash and Sophocles and fires another Goedude directly at them. Fortunately, Metang intervenes and strikes Golem several times with its clawed arms. Golem and Metang exchange intense stares, and before long, the pair engage in a test of strength against each other, while Ash's side and the Geodude and Graveler spur on the competitors. Golem sees its opportunity and punches Metang into the cave's ceiling. Metang quickly recovers itself and reveals its brand new iron sand eyebrows and mustache. Golem feels its face for a moment and quickly realizes it is missing its distinct facial features. The Geodude and Graveler quickly switch sides and cheer for Metang as Rotom explains that the Geodude line value the iron sand features as an indicator of strength and leadership. Golem is frustrated, so Metang returns the iron sand fragments back to it in the form of a mohawk. Metang continues to attract and repel the iron sand from itself and Golem, showing off various facial hair styles. Golem collapses in exhaustion and Metang is declared the winner. As a gesture of goodwill, Metang restores Golem's iron sand facial features to its original style. Rotom takes a commemorative photograph of Metang and Golem for its own database.
Ash, Sophocles and Kiawe reunite with the girls and report to Lusamine that the rock hunters' excavations for Spark Stones led the Geodude and Graveler to flee to the surface and hence the drastic increase of magnetic activity around Wela Volcano. Lusamine is grateful for the Ultra Guardians' efforts and states that she will organize patrols for the Wela Volcano area. The Hikers overhear the conversation and volunteer themselves as patrol agents. The Golem from before then reappears, and, in a strange turn of events, lets itself be caught by the Hikers. The trio of Hikers are overjoyed as they, their Magmar, and their new Golem happily dance around in a circle.