"Werewolf Monster's Huge Murder Party" (怪人狼男の殺人大パーティー Kaijin Ōkami Otoko no Satsujin Dai Pātī) is the thiirty-ninth episode of the original Kamen Rider TV series and the franchise's first Christmas episode, which aired on Christmas Day in 1971.
On a moonlit night, two drunk office workers are stumbling home from an office party with one of them named Urabe stopping and going off to find a bathroom. After waiting a minute or two, his co-worker has to go too and then stumbles over Urabe who is lying unconscious. The man goes to check on him, only for Urabe to start turning into a werewolf. The co-worker tries to flee from the werewolf but he catches him and bites his neck, killing him. The werewolf is then surrounded by Shocker Combatmen and Colonel Zol arrives, ordering the Combatmen to capture their "valuable test subject". The Combatmen struggle to capture the werewolf as it fends them off, but Colonel Zol uses a blowgun to tranquilize the werewolf and the Combatmen capture him. The leading Combatmen says that the results of the "Wolf Virus" are impressive, but Colonel Zol berates his subordinate for letting his test subject escape and run around the city, thus potentially tipping off their enemy Kamen Rider to their activity. He orders his men to dispose of the corpse and all traces of evidence that could be left behind. As Colonel Zol oversees this, he hears a noise and then finds a child's shoe and a girl's doll. He thinks that the doll belonged to the dead man's child as a Christmas present, but as he walks away, a little girl is seen hiding from him, upset that Zol took her doll and slowly sneaks away from them.
At the Midori Kusa Orphanage, Kazuya Taki, Yuri, Tobei Tachibana and Hayato Ichimonji are helping decorate the Christmas tree for the kids. Kazyua asks a boy what he wants for Christmas as if he's been good, Santa will bring it. The boy responds by saying he wants to meet Kamen Rider more than seeing Santa with the girl next to him agreeing. Hayato (who is secretly Kamen Rider), is seen with a reluctant look on his face, but his friend Kazuya promises that Hayato will bring Kamen Rider here with Hayato finally agreeing. As they finish the tree, the excited children tell Ms. Sanne that Kamen Rider is coming to visit them for Christmas instead of Santa. Ms. Sanne is concerned, asking Hayato and Kazuya if it is okay making such a promise. Hayato says he would never do anything to shatter the dreams of children. Kazuya wonders where Kumi is and Ms. Sanne says that she came down sick with a fever last night. Hayato goes into her room to check on her and she tells him a "wolf man" took her doll, with Hayato at first thinking she is pretending. He says she should ask Santa for a new doll, but Kumi gets upset and says there really was a wolf man and thinks that Hayato is calling her a liar like everyone at the Orphanage. But, Hayato says he believes her as he knows she doesn't lie to anyone. Kumi asks if Hayato can get her doll back from the wolf man, with Hayato promising to find it for her. He then tucks her into bed and wishes her goodnight.
At a hidden Shocker base, Colonel Zol realizes that the doll didn't belong to the dead man after examining it, as the doll looks old and worn. He then orders one of his men to give him the shoe they found. He examines it and finds the name Kumiko Hayase is on it, as is the name of the orphanage. He realizes this means that there was a witness last night to thier capture of the werewolf and the disposal of the corpse.
Hayato and Kazuya are at the underpass of the bridge where Kumi lost her doll, looking for it. Kazuya asks Hayato if he really believes her story about a wolf man, with Hayato saying he believes it because it comes from a child. He also mentions that a police report was made that two men went missing in the area. Kazuya thinks this is pointless but Hayato spots something: The shoe of the dead victim. This confirms Hayato's theory that Kumi was a witness to something and her fever and illness was stress induced. A policeman walks by and inquires what the two are doing there, with the two saying they are looking for a missing doll for a little girl. The policeman says he hasn't seen any doll and they are not permitted to be here. Hayato and Kazuya apologize and give up the search, leaving on their motorcycles. After they leave, the policeman is revealed to be Colonel Zol in disguise, who now has the information on the doll and the fact that Kamen Rider is now involved.
At the orphanage, Ms. Sanne has dozed off looking after Kumi and then wakes up to check on the other children. She notices a door she thought she had closed is open and goes in to check, only to be captured by Shocker Combatmen and interrogated about where Kumi is. Ms. Sanne tricks the Combatmen and tries to escape but the werewolf is there waiting for her. Ms. Sanne faints and the werewolf abducts Kumi from her bed. Before he can leave with her, Hayato and Kazuya arrive and upon seeing him know that Kumi was right all along. They then realize that the so called "wolf man" is in fact, a Shocker cyborg. The Wolf Man threatens to kill the child if they come closer, but Hayato laughs at him and says Wolf Man must have terrible eyesight. Wolf Man undoes the blankets and it is revealed to be Goro, Yuri's little brother, who teases the Wolf Man and then escapes his grasp. Hayato asks Wolf Man why the cyborg is targeting a child but the Wolf Man calls for his Shocker Combatmen to come and attack the three. Kazuya fends off some Combatmen while getting to him motorcycle with Goro and then rides off to safety. Hayato dodges Wolf Man's attacks and then transforms into Kamen Rider. He takes out a Combatman and the engages Wolf Man, then leaps up tries to finish him off with his Rider Kick. Unfortunately, Wolf Man dodges it in the air and makes his escape after Kamen Rider falls to the ground. Wolf Man shouts that he will kill Kamen Rider next time.
Kumi is safe at the Tachibana Racing Club, playing cards with Goro and Hayato. Tobei says this is all thanks to Hayato's faith in children that Kumi is safe. Kazuya is infuriated that Shocker would try to kill a child just for stumbling onto them by accident. Kumi says she overheard Zol say Wolf Man was just a test subject as she heard eveything that went on but she was so scared she couldn't move until they had left. Tobei and Kazuya ask her if there was anything else important that might help and she tells them she heard the words "Operation: Wolf" being spoken. Yuri gets a coded transmission from the FBI's New York branch, Kazuya listens to it and says it is intel about an intercepted decrypted cipher from Shocker about Operation: Wolf. A Shocker Commander will appear at the Tanezawa district at precisely 1:00PM. Kazuya's superiors order him to investigate and Hayato decides to accompany him.
At a field in the Tanezawa district at 1:00PM, a helicopter prepares to land and a car is waiting for the Shocker Commander. Kazuya and Hayato stake out the site from a distance as the Shocker Commander gets out of the helicopter, then go to capture him to get information about Operation: Wolf. They take out his guards but the Commander flees before the two can get to him. Hayato uses his cyborg super strength to grab onto the helicopter and then climb up, knocking out the Commander and the pilot. The helicopter crashes and explodes after Hayato jumps out and Kazuya helps him up. Kazuya then shows him a briefcase he found in the car, which contains a KKK-like robe and mask and a formal masquerade party invitation from Shocker to celebrate the start of Operation: Wolf. Hayato says this sounds like a fun party to crash and Kazuya agrees, planning to sneak into the party to discover more about Operation: Wolf.
They drive the car around until they are stopped by a patrol of Shocker Combatmen, One of them in the robe disguise, asks them where the party is located. The Combatmen ask for his invite as identification, then escort him to the hidden Shocker base. Once inside, the guests of the party stand around a table with a candlelit banquet as Colonel Zol greets them. Zol says that the "foolish humans" are celebrating Christmas today, but if Operation: Wolf is a success, it will be the last Christmas the human race will ever celebrate as the world will belong to Shocker. He also says that as a "Christmas present", he will finally rid Shocker of Kamen Rider and his ally FBI agent Kazuya Taki. Zol knows of the fact the two came in disguise and demands that the guests remove their masks and robes, all but one obey his demand. Pleased with his craftiness, Zol gloats over Hayato that the cipher they sent was fake and the party was a trap. Zol orders his men to find the driver and capture him, thinking that is Kazuya. But it turns out that the man behind the robe is Kazuya! Zol interrogates him as to where Hayato Ichimonji is and Kazuya reveals he is in the storeroom to dispose of the Wolf Virus before fleeing. Kazuya meets up with Hayato who says the detonator charges are set and they run out of the base with Combatmen in pursuit. Before Zol can get to them, the commanders try to protect the Wolf Virus only to be hit by the explosion and for the base to collapse in a fireball.
Kazuya emerges out first and calls for Hayato but is then attacked by a squad of Combatmen that he fights off. Hayato calls to him and goes to try and help only for Colonel Zol to stop him. At first Hayato thinks he will send his lackey werewolf to do his dirty work, but Zol decides to deal with him personally by changing into a cyborg form: Golden Wolf Man. Zol then fires missile projectiles from his claws. Hayato evades and nearly gets killed by a landmine hidden in a ditch, emerging from the ditch and then becomes Kamen Rider. He dodges more of Golden Wolf Man's projectiles and then faces off against him. The two fight hand-to-hand and grapple each other, evenly matched. During their brawl, Golden Wolf Man manages to knock Kamen Rider off and he falls, dangling off a hill. Golden Wolf Man tries kicking Kamen Rider in the head and smashing his fingers so he'll fall. Kamen Rider does but the soft soil slows his descent and he stops midway on the hill. Golden Wolf Man leaps down and wildly starts attacking Kamen Rider but then Kamen Rider gains the upper hand and starts beating him down, ending it with his signature Rider Punch. Zol goes tumbling down off a cliff, the damage causing his self destruct device to activate and he explodes. Kamen Rider stands victorious, finally defeating one of his greatest adversaries.
At Midori Kusa, Christmas snow is falling and the kids are getting presents from Santa (who is actually Tobei Tachibana in a Santa suit). The children are singing carols as they sit to eat Christmas dinner and Kumi asks Ms. Sanne where Hayato is as he promised to bring Kamen Rider. Sure enough, the children hear the revving of a motorcycle engine and look outside to see Kamen Rider arrive on his Cyclone with a bag full of toys and presents for them. He carries the bag over his shoulder like Santa Claus and enters the room. He greets the children and asks Goro to help him hold the bag. He hands out gifts to the kids and hands a very special one to Kumi: Her doll, which he had recovered from the base before it got blown up. Goro checks the bag and says that everybody got their present as the bag is empty. Hayato leaves and goes out into the wintry night on his motorcycle, ever vigilant to protect the world from Shocker, even on Christmas.