Hirai Tarō (平井 太郎), better known by the pseudonym Rampo Edogawa ( 江戸川 乱歩), sometimes romanized as "Ranpo Edogawa", was a Japanese author and critic who played a major role in the development of Japanese mystery fiction.
Rampo Edogawa is fun. He is a good writer, with an amazing imagination and a knack for the grotesque and the erotic. He also had an amazing run as YA writer with the "Shonen tantei" series, which are basically the same as his adult novels but with less blood, limbs and naked skin. So, not so much fun.
I'm actually lying. His "Shonen tantei" is quite fun, and this "大金塊" is no exception. It's more a short novel than anything else (200 pages, but with big moji and drawings, it can be read in an afternoon if you're good (or native) at Japanese), and as that, it deals with things in a breezy manner. Famous detective Akechi and his young follower Kobayashi are called to help the family Miyase. One of the ancestors of the family had hidden some gold without telling where, only leaving a secret message that couldn't be decoded. And now a thief seems intent on finding all the gold for themselves.
The beginning is fun and the feeling keeps throughout the 200 pages. But what you can't forgive Edogawa is the laziness that pervades the novel. Not one of the ideas that appear in the story is new. If you have read any of his other books, you will see that many of the things that happen are taken from other of his novels. Too many actually, which takes from the experience. That's basically the biggest problem with the book, as it is fun to read. But you will be: oh, he used that on "...", and this is obviously from "...". Etc. etc. And that Miyase doesn't remember the second part of the secret message is a head-scratcher.