The episode begins with a student transforming into a hideous creature while a shocked Hiro watches. This is the preview of what's to come!
A day before his class trip, Kiyoshiro and Jellymon are in Hiro's room while Ruli and Angoramon are on remote video. They are discussing the dangers of a Gyukimon, who showed up claiming to be Ryudamon. He says that he just suddenly transformed. Also, he was told by Hokuto(Hiro's father) that if he was ever in trouble, find Hiro.
Angoramon is troubled. He knows that if a Gyukimon bites you then you turn into a Gyukimon. Ryudamon swears that he has never attacked anyone. Hiro suggests they find Bakumon to see if he can help. Kiyoshiro leaves reminding Hiro of their field trip tomorrow.
The next day on the boat/ship ride to their trip's location, Kiyoshiro and Jellymon (performing roll call) are shocked to discover that Hiro brought Ryudamon/Gyukimon. They are not happy about this. That evening, Gyukimon's spirit is beginning to take over Ryudamon. He decides to leave so he doesn't hurt Hiro.
Once at the school's lodging facility on the Island, Hiro is frantically looking for Ryudamon! Kiyoshiro freaks out!! Little do they know, Gyukimon begins his attacks starting with Niijima. That evening, when Niijima falls ill, Hiro is asked to bring her some food. This is when the preview takes place where she is transforming. Hiro runs out saying he will get help.
Meanwhile in a short time, Gyukimon has bitten almost everyone on the trip except Hiro and Kiyoshiro. Now they are transforming and going after the two remaining boys. Jellymon returns to help, but blames Hiro for all the chaos. Even Bakumon said it was stupid to bring the Gyukimon to the Island.
Ruli and Angoramon are with Bakumon when they get a call from Hiro. With the signal poor and the boys in danger, they contact Airdramon to quickly get to the Island. Unfortunately, Bakumon is unsure how to change the digimon back. He does remember Bokomon saying the Digivice was the key to that special ability to evolve.
As Betelgammamon and Teslajellymon are holding the Gyukimon off, Symbare arrives on Airdramon and joins the fray. Bakumon says if they can get Gyukimon to remember being Ryudamon, they may be able to use the Digivice to force him back to his original form. Betelgammamon evolves to Canoweissmon where he knocks heads with Gyukimon. A hologram Gammamon finds Ryudamon after slashing through the dark cloud of Gyukimon. The two return to their normal forms, Ryudamon and Gammamon. Ryudamon is happy that he's back to normal.
Bakumon changes everyone back to humans and tweaked their memories of the past few days.