The group has arrived at Mercurimon’s lair only to discover the old man outside. Masaru asks what he is doing there and the old man says to follow him if they want to find Mercurimon. Yoshino and Touma don’t trust him but Masaru does and runs after him.

In Mercurimon’s lair, Ikuto questions whether or not he is a Digimon. Mercurimon tells him he is a Digimon warrior and the humans are the enemy.

The gang enters Mercurimon’s palace and the old man discovers they are being followed by Kuramon and sends them packing with his fishing rod. They continue moving and are located by Tsumemon which are disposed of by Agumon and co.

Gotsumon alerts Mercurimon that the humans are in the palace and Ikuto leaves to take care of the humans. Gotsumon questions why Mercurimon doesn’t take care of the humans and he tells Gotsumon that fighting the humans will turn Ikuto into a true Digimon warrior.

DATS is attacked by Ikuto and Falcomon. The old man is shocked and questions whether or not Ikuto could be someone from his past. The old man hears Masaru call Ikuto “Ikuto” and realizes just who he is (but we don’t find out just yet…) Gotsumon appears saying he has come to help. He causes a cave in and intentionally tries to kill Ikuto and Falcomon along with DATS.

Falcomon and Agumon land together with Masaru hanging below on a cliff-grasping onto Ikuto so he doesn’t fall. The others rise out of the rubble to discover Gotsumon has the old man hostage and they’re told to put their digivices down. The old man says he has something to say to Mercurimon and Mercurimon orders Gotsumon to bring them to him.

Masaru manages to pull Ikuto to safety and the four discover Yoshino’s and Touma’s digivices lying around. Masaru says he’ll finish their fight later and runs off after his comrades. Falcomon begins to wonder if they’re different from the humans who killed Frigimon but Ikuto just runs after Masaru.

In Mercurimon’s lair, the old man says it has been ten years but he is sure Mercurimon remembers him. Touma and Yoshino realize he was part of the expedition. The old man asks about Mercurimon raising Ikuto and why the Digimon are attacking the human world. Mercurimon says it was the humans who attacked the digital world which shocks the old man. Mercurimon tells of how “that man” (Masaru’s father) made a deal to have peace between the two worlds but the humans went back on their word and attacked the digital world, massacring Digimon to the point where they could never be reborn. The old man finds it hard to believe and says the humans never did anything like that. Mercurimon attacks the group. Outside Ikuto attacks Masaru but the fight is interrupted by Mercurimon’s attack.

Inside Mercurimon is about to finish off the group but Masaru attacks him and introduces himself. Mercurimon wonders if he could be the professor’s son but refuses to tell Masaru anything about his father. Masaru returns Yoshino’s and Touma’s digivices to them and they evolve their Digimon to ultimate level. Ikuto and Falcomon appear but Mercurimon tells him to stand down and he rises to fight the three Digimon. Lilamon, RiseGreymon, and MachGaogamon attack but Mercurimon easily takes them down. Masaru tells them to attack together but Mercurimon blocks the attack. The attack destroys a wall behind Mercurimon’s throne which reveals a digital gate. Mercurimon says they were able to slightly injure him and attacks once more, reducing the Digimon back to their rookie levels. The old man pulls out a digivice and causes a Kamemon to realize. He evolves it to Gawappamon and attacks the lair to create a distraction so the group isn’t killed.

The old man tells Masaru he and his friends must escape and gives Ikuto (who was knocked out by the fighting) to Masaru. They barely make it into the digital gate and land in the human world where Satsuma is waiting in a helicopter.