Keiko goes to Urameshi’s looking for Yusuke, but Atsuko tells her he didn't come back yet. He's been going through some kind of training in the mountains for over a month, but he's been phoning his mother. "That proves he's still alive," says Atsuko. Keiko is afraid Yusuke won't come back, but Atsuko dismisses her worries: "He died once and came back, didn't he?"

Keiko is still worried and upset that Yusuke left without any word to her. She's walking on the street with such thoughts when she sees Yusuke, tired, slightly bruised and in ragged clothes, walking in her direction. Unnecessary to say, she's very happy to see him.

In a park, Keiko buys three milkshakes while Yusuke and Kuwabara, in their school uniforms, sit on a bench and talk. Yusuke asks if Kuwabara's arms are healed. Kazuma confirms it, saying that after the spiritual "surgery" performed by Genkai he's a lot stronger, and that he intends to test his new strength on Urameshi. Yusuke retorts that he's also stronger after Genkai's training.

Yusuke tells him about the arduous practice. He had to stand upside down for twelve hours, supporting his weight on his reiki-active index finger over a pointed stake. He also learned (the hard way) how to defend himself from powerful energy wave attacks. Kuwabara says he's looking forward seeing Yusuke's new abilities.

Keiko arrives with the milkshakes and asks what Kuwabara wants to see. Yusuke nervously feigns, "Ahn... it's... aaa... a movie. Kuwabara was telling me about this movie he wants to see..." Keiko suggests that they all go to the movies then.

On the way to the theater, Yusuke senses something. He apologizes to Keiko and tells her to buy the tickets while he and Kuwabara go buy something. When Keiko asks why she can't go with them, Yusuke says it's a "man thing". He runs away, hauling a puzzled Kuwabara by the hand.

After turning around the corner, Yusuke lets go of Kuwabara's hand and tells him they're being followed. Five gray-skinned boys in school uniforms are indeed coming right behind them. Yusuke and Kuwabara guide them to a dead-end alley, where they can fight in peace. But the strange boys have pocketknives.

Yusuke and Kuwabara fight them with punches and kicks at first, but when the boys get up to attack again, muttering, "Kill... kill... kill... kill...", Yusuke decides it's time to use one of the tricks he learned from Genkai. His clenched fist starts to shine, and he punches the air yelling, "Shotgun!" The five boys are hit at the same time by a bluish white energy and fall unconscious.

Kuwabara senses a strange presence behind them and spots a figure wearing hat and overcoat spying on them. The two boys run after the spy, but before they can reach him he's knocked out by a baseball bat held by Botan. Kuwabara is glad to see the beautiful ferrygirl again.

The hat has fallen; the spy is a demon. Botan says he serves the group Yusuke will have to face in his next mission. Yusuke protests: "Hey, wait a minute! I just came back from the training and you already have another mission for me? That's absurd, I'm not Koenma's slave. That's abuse!"

Botan tells him that Koenma received a threatening letter from the Four Holy Beasts, demanding that they be allowed to live in Ningenkai. The Beasts are cruel and dangerous; they built a castle in their hiding place and shelter many criminals of other worlds, creating the lawless City of Beyond.

Botan indicates the five boys lying on the ground: an insect comes out from the mouth of one of them. She explains that it's an insect from Hell, a parasite that feeds from melancholic hearts. The Beasts spread millions of those insects in Tokyo. The humans infected by the insects become rebellious, violent and murderers.

Yusuke suggests that the population should be warned about the insect menace. Botan: "Impossible. It would be useless, Yusuke. Normal humans can't see them. All they can see are humans behaving like savage animals." She says that the only way to destroy the insects is destroying the Flute that controls them. She also explains that a barrier surrounds the Beasts' castle so they can't get out. The Beasts want the deactivation of the barrier in exchange for the return of the Flute to Reikai. But at the speed the insects and the infected humans are attacking, Tokyo might only take one day to be entirely devastated. Yusuke's next mission is to sneak into the City of Beyond and destroy the Flute.

Yusuke complains that Koenma is being unfair, expecting him to enter those bandits' den all by himself. "What about me?" Kuwabara intervenes. "Don't I count?" Botan sweatdrops; she completely forgot he was there, listening to everything she said. (Apparently she wasn't supposed to reveal any details of the mission to other than Yusuke.)

Another insect leaves the mouth of one of the fallen boys; Kuwabara smashes it in his hand. He can see the insects and won't admit that any evil damages his hometown.

Botan leads them to an abandoned underground storage and opens a secret passage on the floor — a portal to the City of Beyond. She reminds Kuwabara that this is a mission for a Reikai Tantei; he doesn't have to go. Kuwabara says he's a Tantei too, jumps into the passage and disappears.

Botan gives Yusuke a communication device. He suddenly remembers that he left Keiko waiting at the theater — and she is shown muttering angrily against Yusuke. Urameshi tells Botan to go give her some excuse in his place, and follows Kuwabara through the portal. Botan: "No, no! Yusuke, wait! Don't put me in this mess! I'm not doing a thing! Yuuuuuuusuke!!!" But he has vanished already.

The City of Beyond: a tall, strangely shaped castle built on a plateau, under cloudy red skies. Yusuke and Kuwabara materialize in the air and fall hard on the rocky soil. They see the castle not far away, but strange creatures wearing brown hooded cloaks appear from the ground and surround them, eager to devour the two human boys.

The creatures attack, and Yusuke and Kuwabara defend themselves as they can, but there are too many of the carnivorous creatures. After a brief fight, they are both immobilized.

With a loud thunder and golden energy sparkles, a hole opens in the sky and two spheres of light, one red and the other blue, come flying through, passing over the creatures' heads and scaring them. The spheres land on a tree branch with a big explosion of white light that frightens the creatures away.

Left alone, Yusuke and Kuwabara look up at the tree, wondering what caused the savior shine. From the branch, a voice says, "It will be a hard battle. Do you need a hand?" Then another voice: "You're doomed. I think your powers are insubstantial." The owners of those voices jump down from the tree: Kurama and Hiei.

Yusuke is surprised to see them again. Hiei says Koenma didn't trust Yusuke to complete the mission and sent them to help. Kurama adds that by that collaboration they'll have a better chance of being absolved in their trial. Yusuke is happy with the news and introduces the two thieves to Kuwabara, who welcomes a helping hand. "Make no mistake," warns Hiei. "I don't know about Kurama, but I'm not here to collaborate with you. I'm gonna fight the Beasts because they stole many treasures from me." Kurama smiles at that statement.

Kuwabara dislikes Hiei immediately: "What's with you, little spiky? Your attitude is annoying. What a cynical!"

"You imbecile," replies Hiei in a low tone. "Do you want to die?"

Kuwabara jumps on him, but Hiei blurs out of the way and appears next to Yusuke: "What about you, Yusuke? Did you think I forgot? Be prepared, I'll have my revenge." Kuwabara gets on his feet and tries again to punch Hiei, who once more blurs out of the way and steps back beside Kurama. "Cut it out, Hiei," says Kurama. "Set your accounts after the mission is complete."

"All right!" exclaims Yusuke. "The more allies the better. Let's go to the castle."

As they walk towards the eerie building, the four Beasts discuss the new menace. They're not worried, not seeing much power in any of them. They're sure they won't even get to pass through the Gate of Treason.

The boys arrive at an entrance that looks like the open mouth of a skull. Hiei and Kuwabara keep on with their bickering while they step inside, crossing a long corridor.

Suddenly a demon — an eye with tentacles and bat wings — appears and welcomes them to the castle, but warns that they have to go through a test before entering. With a tentacle, the eye-demon pushes a lever and the ceiling falls on the boys, who try to hold it up with their hands.

"Tell me, boys, is it heavy?" asks the eye-demon, disdainfully. "This gate is sensitive and intelligent. The more strength you use to stand its weight, the more pressure it applies on you. Use all your strength. If one of you weakens, all are smashed. If one betrays the others and escapes, the others die. Together you can keep the pressure, but you'll run out of energy and die eventually. Only one, the traitor, will be able to enter the castle. It's your choice. Do whatever you think best."

Kuwabara yells against the eye-demon and, losing concentration, lets the ceiling fall down an inch more; Hiei reproaches him for it, and Kuwabara replies that if someone there is a liability, that's Hiei. Yusuke tries to calm Kuwabara down. "If you don't trust me," says Hiei, "what if I betray you?"

"Knock it off, Hiei," says Kurama.

While the eye-demon laughs, Yusuke tries to think of a way out.