When 1930s Tokyo is threatened by a master thief who can disguise himself to look like anyone, and laughs at the law, the people of the city have nowhere else to turn but Japan's greatest detective, Akechi Kogorō. Unfortunately for Tokyo, however, Akechi Kogorō is off on overseas business, so it becomes the job of his 12-year old assistant, Kobayashi Yoshio, to track down the thief and desperately keep him at bay until his mentor returns. In the spirit of Sir Arthur Conan Doyle's Baker Street Irregulars, a classic thriller by Edogawa Rampo, grand master of Japan's Golden Age of crime and mystery fiction. Filled with disguises, tricks, "A-ha!" moments, and spiced with a unique Japanese flair, it is sure to delight readers of all ages. Will Kobayashi's intrepid band of young detectives be able to outwit the nefarious fiend, or will Tokyo be forever at the mercy of the face-swapping phantom?

底本：江戸川乱歩全集　第1巻　屋根裏の散歩者 (光文社文庫) 光文社

少年侦探团团员泰二发现一名怪异的老人蹲在十字路口画着奇怪的记号，便一路尾随，不料却落入了妖怪博士设下的陷阱。随后，少年侦探们一个接一个地下落不明，原来是他们接连破获大案，歹徒们怀恨在心，伺机报复。为了救出少年侦探们，大侦探明智小五郎大展身手，终于再次挫败了二十面相的阴谋。

A thief is on the loose in Tokyo, a smash and grab artist that targets high-end jewelry stores. The identity of this burglar is no mystery. It's a metal robot, dubbed the "Bronze Devil" by the press. Except with its almost magical ability to appear and disappear out of nowhere, the police are powerless to stop one theft after the other. That can only mean it's time to put master sleuth Kogoro Akechi and the Boy Detectives Club on the case.

天野勇一君の町に、奇妙なおじさんがひっこしてきた。少年たちの前で、ふしぎな奇術をつかう魔法博士はいった。「わしの住む洋館には『ふしぎの国』があるのだよ。」ある日、洋館をたずねた勇一君と小林少年。ところが、博士のおこなう大魔術の舞台にあがった勇一君が、見物客の目の前ですっかり消えてしまった。

The year is 1953. The Korean War is winding down. The Cold War is heating up. The United States detonated the first hydrogen bomb the year before. Godzilla will make his debut a year later. UFOs are appearing all over the world. And in Ranpo Edogawa's latest novel, five flying saucers zoom across the skies of Tokyo. A day after that incident, a woodsman stumbles out of the forest to report the landing of an alien spacecraft in the mountains southwest of Tokyo. A month later, Ichiro Hirano's next-door neighbor goes missing. And then reappears as abruptly as he vanished, claiming was kidnapped by a lizard creature from outer space. That same lizard creature is now stalking the pretty and talented sister of Ichiro's best friend. What in the world is going on? What do the aliens want? And where did they come from? These are the kind of questions that only master sleuth Kogoro Akechi and the Boy Detectives Club can hope to answer.

房総半島の沖合、沈没船で作業をしていた二人の潜水夫が、海中の怪物を目撃する。それは全身が鉄でできた人間とワニの間の子のような怖ろしい姿をしていた。直後、今度は近隣の漁村の少年が同様の怪物と遭遇する。話は変わって東京都、世田谷区。少年探偵団の団員「宮田賢吉」君が、帰宅途中に謎の人物から鉄の小箱を託された。小箱には莫大な金塊を積んだまま沈んだ「大洋丸」の、沈没地点を記した書類が収められていた。

少年探偵団の井上君とノロちゃんは、町で怪しげな骸骨男に遭遇、尾行を開始する。骸骨男はサーカス小屋の中で忽然と姿を消し、その日から小屋の中で恐ろしい出来事が次々と起こり始める。名探偵・明智小五郎と、小林少年率いる少年探偵団の活躍が始まった―。