This is a chapter by chapter summary of Meitantei Marnie.
Chapter 1: Candid camera. Marnie is introduced investigating a peeping tom incident in the girls locker room. Meanwhile, Lloyd investigates a kidnapping attempt. The kidnapper revels in the tears that the parents shed at a tearful reunion with their child. Meanwhile, the camera was planted by a girl's parent, but a third party hacks into the camera. Shiratori is introduced in this chapter.
Chapter 2: Dying message. Marnie investigates the life and death of Yuji on behalf of his friend Nachi, the school jock. Yuji, missing out as he slowly dies, plays a video game with a complex AI. He invents a companion in the image of Nachi and goes on adventures with him. Nachi is introduced in this chapter.
Chapter 3: Doppelganger. A former client of Lloyd asks him to investigate a doppelganger going around with a strange man. The man is a stalker of the client, and creates a sex doll in the image of the client to go with her openly, going so far as to attack Lloyd who was following him.
Chapter 4: A marriage and a funeral. Yurika asks Marnie to investigate a person who she sees floating around at a relative's funeral, and repeatedly saw after that. Yurika thinks its a fateful encounter. Marnie, knowing better, thinks that Yurika is a tad bit dreamy about this. The guy's a funeral otaku. However, Yurika did not mention that the wedding she met him at was not one she was invited to. The two get together. Kataoka Yukito is introduced in this chapter.
Chapter 5: Lost Goods. Marnie catches a thief on camera, and asks the boy Kaneo why. She concocts a scheme for Kaneo to provide gifts for his grandparents. He takes their possessions and hides them. The grateful grandparents appreciate their 'items' far more than what Kaneo could provide if he were to gift new ones. However, it is later revealed that all of the grandparents were dead to begin with and were unaware of it. Marnie passes by the derelict house while searching for Kaneo.
Chapter 6: Intruder. Marnie is requested by Mochizuki Kaede of the Cardigans group with regards to a stalker. An unknown girl had been sneaking into his clique, and Kaede discovers a home invasion. Cameras are installed, and Marnie discovers something hidden amongst his belongings. Kaede is a serial date-rapist, and one of his victims had gone so far as to camouflage as his follower and invade his house to search for evidence of his recordings. As he worries about Marnie, the police knock at his door.
Chapter 7: The Laughing Man. Kosaka from the upper class society and school council requests Marnie to look for his divorced father. He claims to hear him everywhere. It turns out that Kosaka has been listening to his father from the laugh track, and the family estrangement could be traced back to his father's occupation: laughing at home is hard when it's part of your job.
Chapter 8: Penpal. Marnie's father Lloyd is requested to take on the case of a shady politician who wants to look for his lost penpal. The politician is deeply involved; but lied to his respondee about his life. He finally finds his penpal — dead in a hospital. The penpal had lied in response in order to prop the politician up.
Chapter 9: Monster. A red-eyed, white-furred monster started appearing in school. Maehana, a witness, posts a message and it goes viral, even inviting a news crew waiting on Marnie to unveil the true colors of the monster. It actually was a civet afflicted with scabies, but the news crew continues to spread the rumor of an evil monster, aided and abetted by Yurika. Maehana is introduced in this chapter.
Chapter 10: Miyajima-sensei's first crush. Under threat (of having her side-income revoked), Marnie quests through the gym teacher's class to find her crush. The crush had undergone gender reassignment surgery and chose not to contact Miyajima-sensei accordingly. While cameoing in Chapter 9, Miyajima Sayuri is introduced here.
Chapter 11: Bullet. Lloyd's tasked with finding the leading actor of a toy movie for a remake. He's found the actor. The actor... has a few screws loose. The actor's been on the run after running away with the female lead and daughter of the director. The director's looking for the third-rate hack who eloped.
Chapter 12: Grandfather. Marnie figures out that the mysterious man that her friend was looking for was her father. It turns out, Lloyd bears a stunning resemblance to the deceased grandfather, and the friend's sister was distraught. While Lloyd spends time with the sister, the sister eventually asks Lloyd not to return.
Chapter 13: Twins. A serial cosplayer has been moving around the neighborhood, and Marnie investigates (at twice her usual rate!). She finds the criminal quickly, but... which twin is it? The extroverted twin commits minor crimes to relieve stress, the introverted pseudo-Batmans as his hero. Kuroya Yukihiko, who Marnie patronizes for cosplay/patrol stuff, is introduced here.
Chapter 14: Grandfather. Yurika's grandfather had been playing 'Cry Wolf' with Yurika. Marnie finds that quite a few of her clients have also been contacting Lloyd's, only to cancel the request. After a class gathering, members had been trying to mimick the feeling of having someone care about them.
Chapter 15: NTR. Miyajima-sensei comes with a witness account of two friends, one good-natured, one who steals girlfreinds, hence an NTR. After having his girlfriend stolen, the former dates a Yandere and the latter ruins his own life by stealing her as well. Marnie arrives to see the two getting married.
Chapter 16: Shrewd Salesman. The news club takes pictures of the school sports meet. Naturally, this means they come under suspicion after several pictures are auctioned off. One of the members was raising cash for the news club by selling merchandise of the students. The school's news club (and clique) NEWSSITE is introduced here.
Chapter 17: Ten. While riding out, Marnie's bike tyre burst, but luckily, someone else rescues her! Ten hires Marnie to investigate her relative. After an investigation, Marnie discovers cameras near Ten's house, and informs the granduncle that he was being investigated. Marnie discovers that Ten's 'granduncle' was an ex-Nazi on the run, and was captured by Mossad, though she does not tell Ten afterwards.The biking enthusiast Maishiro Ten is introduced here
Chapter 18: Magician. Marnie's friend Maki plays a card trick, and induces Marnie to look for her old Main/Mentor Marcus Marino. It turns out that Maki and her sister were also magicians, but Maki's sister was hospitalised. To motivate Maki's sister to recover, Marcus had used a long-prepared trick to surprise her sister with the greatest trick possible.
