警視庁警部補、古畑任三郎の少年時代の思い出
山梨のある村の中学校に、古畑任三郎という不思議な少年が転校して来た。同じクラスの向島音吉と友人になり、学校内の事件をいくつか解決したことから、村の一軒のあばら家に探偵事務所を開くよう勧められる。当初はさほど依頼を期待していなかった古畑だが、役場の助役の蒲郡、同じクラスの真鍋、寺の和尚と3人の依頼を受ける。また、古畑が心を開いている、科学の野々山先生が宝探しを提案するが、宝は見つからなかった。
真鍋の件では、古畑、向島の3人で、夜の学校に忍び込む。その後、古畑は向島と共に、教頭室の外でわざと騒ぎ立て、森脇教頭から叱られる。その後、森脇は古畑に、君に取って善悪とは何かと問い、自分に刃向かう者が善人であると決めつけてはいけないと言う。
しばらく経って、古畑は、自分と向島が、ほぼ毎日のように事務所を離れなければならなくなっていることに気付く。また、畑のそばに積み上げられた土の高さが日に日に増していた。また、和尚の孫娘の明日香が、檀家に届け物をして帰る途中男につけられ、古畑と向島はその男を追いかけて、上着とシャツの袖に、蒲郡の服にあるのと似たシミを発見する。蒲郡は改築ほどない事務所を訪れて、服を汚していたのだった。
その夜古畑は事務所で穴に落ち、その音を聞きつけた野々山が入って来るが、実は彼と蒲郡、そして和尚はここに集まって、2人の少年を殺すことを示し合わせていた。そして野々山だった。宝を掘り当て、彼らは軍資金をこの事務所の下に隠すため、穴を掘っていたのだった。畑の近くの土の高さが増していたのはそのためだった。しかしそこへ多くのパトカーが何台も止まり、すべてを知っている森脇が事務所に近づいて来た。野々山は警察に連行される前に、古畑の暗号解読能力をほめるが、最初に暗号を解読したのは森脇だった。しかし、敢えて宝に手を付けずにいたのだった。森脇は古畑に、上っ面だけで人を判断せず、心を読むようにと伝える。
和尚も逮捕され、明日香は親戚に引き取られた。そして、古畑も水商売の母親のトラブルから、その後村を去って行った。村を去るまえに古畑は、自分が何度も読み返した『バスカヴィル家の犬』を向島にあげた。
A memory of Ninzaburo Furuhata, inspector of Tokyo Metropolitan Police
A strange pupil called Ninzaburo Furuhata transfers to a junior high school in a village of Yamanashi and he becomes to make friends with Otokichi Mukojima. As he solves some troubles in the school, he is recommended to open a detective office in a tumbledowan house. At first, he doesn't expect any request but three people as Gamagori who is a headman's assistant of the vilage, Manabe who is a classmate of Furuhata, a priest (osho) of a Buddhist Temple.request him to solve their troubles. And Nonoyma who teaches science at his junir high school to whom Furuhata opens his mind proposes him an idea of treasurｙ hunting though the teasury is not found.
Furuhata and Mukojima steal into the school when Manabe requests them to search his trumpet left in the school at nighttime. After finding it, Furuhata and Mukojima make a noise on purpose outside the room of deputy headmaster and are scolded by Deputy Headmaster Moriwaki. After that he asks Furuhata what is right and wrong and tells him that he should not label those who is against him as bad people.
After a while, Furuhata finds that he and Mukojima are obliged to be away from their office alomost every day. Besides it, the height of the soil piled up near fields increases day by day. And Asuka, granddaughter of osho is chased by a man on her way from one of osho's parishioners. Furuhata and Mukojima chases him and find the smudges on the cuffs of his jacket and shirt. They are similar to those of Gamagori who stained his clothes when he visited their office whose remodeling was just finished.
That night Furuhata falls in a holre in his office. Then Nonoyama who hears the sound enters but he and Gamagori, and osho arranged meeting there beforehead to murder the boys in reality. It's them who stole the treasury and plan to hide in the hole that is digged by themselves and that's why the soil near field increases. But many patrol cars arrive there and Moriwaki who knows everything approaches the house. Before being taken to the police, Nonoyama appreciates Furuhata's ability of decryption but Moriwaki says that it's him who decrypted it first but he dared to leave it untouched. He tells him not to look only at the surface but read a person's mind.
Asuka is adpted by another relartive because of the arrest of osho. And Furuhata himself also leaves the village due to a trouble of his mother who works in a nightclub. Before leaving the house, he gives "The Hound of the Baskervilles" read by him many times to Mukojima.
