Enredo

Arsène Lupin III appears to be undergoing a Jekyll-Hyde crisis - he alternates between a shrewd but kind character and a cruel vicious character. Will he manage to control himself?

Arsène Lupin III learns he is suffering from transformation sickness, where he switches from his shrewd but good-hearted nature to a cruel, heartless character. This Lupin goes around committing brutal crimes with little or no regard towards crushing innocent lives. After numerous crimes unworthy of the name of Lupin, Lupin's self-confidence is completely shattered and in his depression contemplates taking his own life, but due to various factors, cannot succeed at dying. Then he learns that he was himself while his alter ego was committing a crime... and a hunt for his double begins.—Tenchi

Lupin is believed to have transformation sickness which makes him change into a cold blooded murder and commit crimes the actual Lupin would never commit. The problem is you have no memory of what you did during the transformation. And Lupin finds it hopeless and was thinking of dying to prevent anymore trouble. But Fujiko won't let him till she knows whether those crimes were done by Lupin or not.—J LeGault

A wealthy man named Fugo gets a note from Lupin III that he will be visiting to steal a jewel called the Star of Versailles. Soon, he finds a man in Lupin's clothes and imitating his voice in his house. The Lupin look-a-like shoots Fugo dead and steals the jewel. The next morning, Lupin and his gang watch the news on the TV. Lupin is sure that this is an imposter who fabricated his fingerprints, but Jigen and Goemon are skeptical. Lupin decides to move onto their next target, a ruby called the African Queen, owned by a man named Zenial. At Zenial's place, Fujiko tries to steal the African Queen, but the Lupin imposter kills Zenial and beats Fujiko to the ruby. At a cafe, she confronts Lupin and doesn't believe he's innocent. Lupin is just angry that Fujiko tried to steal the African Queen without him. A man named Dr. Nomil, who was an acquaintance of Arsene Jr., approaches and invites Lupin to his place. At his house, Dr. Nomil offers Lupin a drink. In another room, he shows Jigen and Goemon what's happening in the other room. As Lupin drinks, he clutches his throat and groans. He appears to turn into the evil-looking man from earlier. Dr. Nomil tells Jigen and Goemon that Lupin has "Disguise Syndrome", an illness which causes his face and personality to change at a certain time of day, which in this case is midnight, and has no memory of each transformation. He convinces them that Lupin was the one who killed Fugo and Zenial. Jigen and Goemon leave and thank Dr. Nomil. As soon as they leave, the Lupin imposter comes out with a projector; the fake Lupin had put film in front of the window to trick Jigen and Goemon, while Dr. Nomil had spiked Lupin's scotch to make it look like he was actually transforming. They go out into the lounge where Lupin is sleeping soundly, and affirm that now that step one of the plan has worked, they're ready to move onto step two. Lupin wakes up in a hotel room, to find to his shock the corpse of a young woman in his closet. He remembers he left a tape playing in his room the night before. He watches the tape playback and sees to his horror that his face has changed. He believes he really did kill the woman, named Francine. Lupin goes to see Dr. Nomil again. Nomil diagnoses him with Disguise Syndrome, and Lupin leaves, despondent. Watching the news and seeing himself get blamed for twelve murders, Lupin asks Jigen and Goemon to kill him. They agree and try to, but Lupin keeps dodging out of habit. His friends give up. Out in a small clearing, Lupin tries to hang himself. However, Fujiko shoots the rope and saves him. She assures Lupin that he is not a killer, and forms a plan with him. At Lupin's hotel room, Fujiko ties him to a chair. Midnight strikes, and Lupin appears to transform. However, he only sneezes. Fujiko realizes that Lupin has been tricked. This revelation lifts the thief's spirits. Elsewhere, Dr. Nomil tricks Zenigata with the same altered tape Lupin watched in his hotel room. Lupin, in disguise, stakes Dr. Nomil and the serial killer out at a cafe. Then, disguised as Dr. Nomil, he tricks Zenigata into thinking Disguise Syndrome has spread to Jigen as well, using special film they hid in the Inspector's binoculars, and has the two criminals arrested. Lupin and Fujiko watch the police drive away. Fujiko notes it's 12 O'Clock. Lupin pretends to transform and kisses Fujiko. She slaps him away, telling him it's 12 noon, and walks off. Lupin bounds after Fujiko, asking her to buy him lunch.