Five years after the events of the main story, a 23-year-old Koyomi Araragi has passed the national police exam and become a police officer. Rather than joining a conventional division, he is assigned to the newly established Hearsay Department of the Naoetsu Police Station, a special unit created by the specialist Izuko Gaen to suppress strange rumors before they can evolve into full-blown oddities. The story is set in his hometown, where he once again finds himself mediating between the human world and the supernatural. During his four-month training period, he works alongside a team of unusual colleagues, each harboring their own connection to the inexplicable.

The narrative is divided into four arcs that follow Araragi and his partners as they investigate seemingly minor incidents. The first story, Zenka Mermaid, partners him with Zenka Suo, a 26-year-old policewoman who was saved from a fatal traffic accident by eating mermaid flesh. Her immortality comes with a severe drawback: any contact with water causes her body to transform into a fish, with the specific species depending on the type of water. They are called to investigate a series of drowning incidents involving children in a local river. With the help of Shinobu, who remains bound to Araragi, they uncover that the soul of the first victim has merged with the river itself and has been unconsciously dragging other children into the water while desperately seeking help. Zenka uses her transformed body as bait and her mermaid song to allow Araragi to reach the lost soul.

The second story, Nozomi Golem, follows Araragi and Nozomi Kizashima, a 29-year-old police inspector who appears to be a middle schooler. She died of an illness as a child, but her grandparents bound her soul to a clay golem, making her effectively immortal. She cannot age and must constantly hydrate her body to prevent it from cracking. They investigate a series of attacks at Naoetsu Private High School, Araragi's alma mater, where students have had their uniforms slashed without injury. Consulting the mysterious Ougi Oshino, who now resides as one of the school's seven mysteries, Araragi deduces that the slashing is not the work of a kamaitachi sickle weasel but a purely human act committed during gym class when the uniforms were unattended.

The third arc, Mitome Wolf, focuses on Mitome Saizaki, a 29-year-old police inspector descended from a line of werewolves. Unlike traditional lycanthropes, she transforms not only by the full moon but by looking at any round object, though she can resist the transformation through sheer willpower. She is assigned as a bodyguard to Tsubasa Hanekawa, who has returned to town. The story explores the path Hanekawa has taken since leaving, and how Araragi reflects on their relationship. The final story, Tsuzura Human, centers on Tsuzura Kouga, the only completely ordinary human in the Hearsay Department, providing a contrast to the other members and highlighting the unique nature of the unit.

Throughout the volume, readers learn the fates of other major characters. Karen Araragi lives alone with her brother and has become a police officer herself, growing to over 180 centimeters tall. Suruga Kanbaru is studying to become a sports doctor while still playing basketball. Nadeko Sengoku has left the city and debuted as a manga artist under a pen name. The most significant development involves Hitagi Senjougahara, who is featured on the cover wearing a white bridal kimono. The novel explores the paths that Araragi, Hitagi, and Hanekawa have each chosen at age 23, and the feelings that Araragi ultimately wishes to convey. The Hearsay Department itself represents Gaen's vision of bringing the practices of supernatural specialists into the public sphere, collecting people with past experiences with oddities into one organized unit.