Yamaki Hanako, a single veterinarian who has passed 40, is the director of "Hachimaki Animal Hospital", following her father's footsteps at her parents' home in the downtown area where she was born and raised. She lives with her younger brother, Masakazu, who is a detective in the Investigation Division, but her aunt, Suzuki, who wants to live with her, rolls in and the Yamaki family becomes noisy. The owners who came to see Hanako formed a "dog club" and often held meetings in the park. Members included Aizawa Mitsuko, a jeweler, Maekawa Noriko, a mature Masuda couple, and Kaneko Mitsuru, the owner of a small dog. Hanako visits the park with Suzuko and learns that a member, Shinkoji Fusae, was burned at her home and was hospitalized. Fusae was the owner of a dog called Lucky. That night, Hanako, who is on her way home after her home visit, is about to come into contact with a car driven by Maekawa. The car ran away without noticing Hanako. Shortly thereafter, she ran into a crowd, found Lucky being hit by a motorcycle, and took her home for treatment. Hanako realizes the deep bond between the dog and her owner, wondering if Lucky had gone out in search of her hospitalized Fusae. The next morning, Hanako, who is lucky enough to visit the Shinkoji family, discovers Marie, a popular manga artist and sister of Fusae, who is bleeding from her head and dying in her room. Police, including Masakazu, who rushed to the scene, learned that the crime time was past 10 o'clock last night, and that the neighbor had heard the dog barking quite violently at that time. Hanako, the first discoverer, suspects she had left the house and had an accident after Lucky barked at the criminal.