At Mukogaoka a fairground full of ferries wheels and spinning tea cups thee is a place called the Flower Orangery. Yukkie takes her little brother into there but finds the plants to be creepy so she wants to go home. Kenji, her little brother refuses then walks off to a nearby plant. Kenji wants to know what the plant is called. The sister looks it up in her book, it’s a Sarracenia and it’s carnivorous (wait.. is this the little shop of horrors?)
Kenji walks off, while Yukkie continues to read in her book about the Sarracenia. Then a monster shows up, a vine wraps around Yukkie’s neck as the monster drags her into the soil. Kenji watched it happen but is unable to help. He leaves the building crying, soon he runs into Ruriko and Hiromi as they were on their way to the Flower Orangery.
Kenji tells them that his sister was eaten by a flower. They take him to go see Hongo and Tachibana. Hongo asks if they took Kenji to the park staff, so that they could look for Yukkie. Ruriko says that because of what Kenji said about his sister being eaten by a flower.. the staff didn’t take him seriously. Hongo asks IKenji where he last saw his sister, he replies promptly that he last saw her at the greenhouse. The bar tender doesn’t believe Kenji either, telling him that he shouldn’t make up stories.
Hongo however, believes that Kenji is telling the truth. In fact Yukkie isn’t the first person to go missing near that botanical garden. Ruriko tries to comfort Kenji by saying that his sister may have just gone home. She wants to take Kenji home as Ruriko is sure that his mother is worried about him. Kenji says that he doesn’t have a mother and when asked about his father, he tells Ruriko that he’s dead. This means that Yukkie is his sole guardian.
Ruriko is shocked to hear that Kenji has no parents so she says that maybe Yukie has gone home. Hongo says the same, then asks Kenji where he lives. Kenji lives in Seishunshou in Ikuta. Hongo says that he, Ruriko and Hiromi will take the boy back home.
The boy practically skips back home but after calling for his sister when he gets there and getting no response.. Kenji starts crying again. Hongo looks around noting that though the apartment is small, Yukie and Kenji live their life to the fullest. He wonders what exactly happened at the botanical garden. Hongo looks at a picture of Yukie and Kenji together while he thinks on the matter. Hongo tells Kenji to stop crying, then grabs his hands only to accidentally end up hurting Kenji. Hongo mad at himself sees the changes to his body made by shocker as something that now prevents him from comforting children.. he leaves the apartment.
Kenji doesn’t understand why Hongo is upset so he follows after him with his toy airplane. Kenji catches up to Hongo and gives him the airplane in return for Hongo’s help to find Yukie. Hongo is touched by the gift and swears to Kenji that he will find Yukie, he then runs off with the airplane to do just that.
Hongo arrives at the botanical garden to find that the Sarracenia has gone, there are traces of its escape though. Hongo figures out that Yukie must have disappeared with the plant. Shocker thugs show up, they throw a dagger at Hongo. The dagger misses him but ends up breaking the airplane he was given. The Shocker thugs run away but an angry Hongo is in pursuit.
There’s a car chase with Hongo following close behind on his motorcycle, partway through the chase.. he transforms into Kamen Rider. Hongo manages to get in front of the car forcing the thugs out of it for a fight. Hongo manages to get a chokehold on one of the thugs but the others run away.. not without throwing one last dagger at Hongo (it misses).
Yukie wakes up to find herself surrounded by Shocker thugs as well as the Sarracenia plant monster. Yukie also sees someone else being experimented on but the view isn’t very clear. Yukie wonders about her whereabouts. The plant looks like it is about to interact with her but is interrupted by a thug that reports Kamen Rider has captured one of their men.
A moment after the plant monster is informed of the situation the Shocker boss comes over the PA system. A Shocker thug says that No.3 has been captured. The Boss says that according to Shocker law, Sarracenia must eliminate No.3. Yukie finally demands to know where she is as Sarracenia is about to leave. It’s the Shocker Boss that answers her over the PA system. Yuki is in the underground hideout of Shocker’s Sarracenia.
It turns out it’s a man in the machine that has already been prepped with an injection for the remodelling test to see if he can become a Shocker cyborg. The Boss says that 50,000 volts will be sent into the man’s body and if he survives then he will be sent to the cyborg laboratory to become a Shocker Cyborg. However the man dies and then Yukie is informed that she will be undergoing the process soon herself.
At the apartment, Kenji wakes up from a nightmare calling for his sister. Ruriko comforts Kenji by telling him that Hongo will find his sister and everything will be all right. Ruriko then tucks Kenji back into bed. A moment later the buzzer for the apartment rings. Hiromi answers the door to find Hongo with an unconscious Shocker thugs slung over his shoulder. Hongo asks if anything happened while he was gone but the answer is no. Hongo is tying up the henchman when Ruriko comes out of the bedroom.
Hongo greets Ruriko by saying that he brought home a guest, from Shocker. Ruriko is surprised to hear about Shocker’s involvement, Hongo tells them that Yukie has been kidnapped by Shocker. Hongo then wakes up the thug so he can get the location of the hideout from the Shocker Thug.
It must have worked because the next we see is Hongo on his motorcycle driving towards the hideout. We get a brief glimpse of the thug knocked out and another glimpse of Yukie being put in the machine. Yukie is still conscious despite the predatory drug unlike the last victim. Hongo uses his motorcycle to get past the guards outside before fighting his way as Kamen Rider inside the complex, rescuing Yukie. Yukie informs Hongo that the Sarracenia plant went outside to kill a captive.
Back at the apartment, Ruriko comes into the room to find Hiromi and Kenji hiding away from the window. She asks them what’s wrong. Hiromi says that there was a plant monster at the window. Kenji insists that it’s the plant that ate his sister. The three of them hide in the bedroom and watch as the Sarracenia plant kills poor No.3 in the living room. The monster then turns towards them.
The monster grabs Ruriko and begins choking her with its vines. Luckily Kamen Rider shows up in time to save her. Hongo forces Sarracenia outside to fight. It’s not long before he defeats the monster with a Rider Kick thus saving the trio. Kamen Rider then pats Kenji on the head before riding off. Moments later Hongo shows up with Yukie reuniting brother and sister while the trio of friends watch he heartwarming moment.
The next day or at least quite some time later..Yukie and Kenji greet Hongo on his way into the university. Hongo repeats a similar gesture he did the night before as Kamen Rider, when Kenji comments on it though Hongo is quick to cover saying that he’s not Kamen Rider. Yukie and Kenji wanted to thank him for his help rescuing Yukie. Hongo tells her that Kenji even gave up his airplane in order to find her. Yukie is surprised by this and promises to buy her little brother another one. Kenji isn’t sad about the lost of his first toy though because it was an agreement between two men and it got his sister back.
The two leave and Hongo feels a twinge of jealousy that he can’t have that kind of relationship with anyone. He’s convinced that because he’s a cyborg.. he can’t have love (blatantly untrue!). Hongo is convinced all that awaits him is a long and gloomy battle.
Roll those end credits! That’s the end of Kamen Rider: Episode 4!!