Dan Morihiko is the greatest detective in Japan but due to problems he's pretty much retired. Now he works as a teacher of the Dan Detective School (DDS), an institution that only students with a keen eye and mind are allowed to enter. The DDS has different tiers of classes, from the worst class in ~D to the greatest class in Q (btw this series only focuses on A and Q classes). The Q Class, in other words the "Qualified Class", is personally taught by Dan Morihiko and it's meant to give a birth to the successor of Dan Morihiko as the greatest detective in Japan.
Our main characters are the five kids who get to the Qualified Class. The protagonist is known as Kyuu. A green/black-haired slightly perverted middle school boy that seems to be able to solve any case like nothing. At the beginning of the series we learn that Kyuu was saved by some man in his youth which was what caused him to want to become a detective. For the other main characters we have the pink-haired girl (apparently when they talk about hairs in this series, she doesn't have pink colored hair actually but the colors are meant for a shounen series I guess) so these characters) Minami Megumi who has an ability of photographic memory that's often used in cases, the lucky martial arts master Kintarou (whose father is a high-ranking cop), the rich-kid Kazuma who loves to create games and use a computer. I've read 8 volumes of this series and Kazuma's been hilariously neglected so far though (he did get one 2-chapter case in the 8th volume I believe finally), the authors don't seem to care much about him. And lastly there's also the genius character Ryuu Amakusa, who's meant to be the character that has to do with the overarching storyline that this series tells. Ryu is meant to have the air of a 'rival' character to Kyu, but he's not. He's supposed to be great at every subject and stuff like that but in deductions Kyu seems superior.
As I mentioned I've read 8 volumes of this series so far and I'm kind of surprised at how little of the main story there's been. There's like only one mention towards something every volume, maybe. The plot is about this criminal organization named Pluto that sells supposedly perfect murder plans and that has the supernatural ability to hypnotize people to kill others. But I believe we actually got anything of this organization in Volume 5 for the first time. Where I'm at right now there has really not been anything about Ryu and this plot connecting to each other either, we just know that there's some perhaps dangerous woman taking care of him and she was ordered to do so by Ryu's grandfather.
But there was this one "case" where Kyu and Megumi get trapped underneath a mysterious trap door created by someone for some reason in the school. They got locked up in a dangerous jail cell by a Pluto member that also threw a poisonous snake in there with the two. This odd prison was presented in a creepy fashion. This story worked well to create some extra tension to the story as a long time ago someone was being held in the cell, but we don't get to know who it could have been.
The DDS contains a badge (The "DDS Badge") that contains useful tools and has absolute authority in crime scenes. Every cop bows when the students show their DDS badges, but as criminals often attack detectives our characters are kind of sort of nerfed from using those all the time to get information about the crime from the cops. In the DDS, while the Q Class consists of the best of the best, the A Class seems to be far more experienced than them in solving harder crimes. They're also all like university students and geniuses, supposedly, while Q Class is bunch of middle school students. There's some rivalry between the two classes as there's a risk of the Q Class students falling down in class tiers, while A Class students can take the place of a Q Class member, provided if the Q Class members won't be able to solve cases and pull off during exams.
One thing I like about this series is how things build up from one case to the other. Like there's the entrance exams to the school, then you get to the school, then you go to your first class which leads to going to the first big case (the Kamikakushi Village Murder Case is probably the case most people talk about this series). Right now I'm up to volume 9 but the next case seems to consists of all of volume 9 and some of 10 so I'm not really going to read the case in a while as these looong cases really burn me out.
My favourite cases so far are:
1) The Occultism / Spirit Summoner Murder Case (Vol. 5) - Great culprit and answer to the case & introduction to Pluto. I felt the cast was way too bloated (didn't bother really analyzing the hints because of that), but it was handled well.
2) Kazuma's Case (Vol. 8) - Answer to the trick is nonsensical but I was very annoyed when Kazuma didn't really do anything worth mentioning for 8 volumes until this story. We also get to see a really cool intent of good-will from Kazuma (as he's presented as a jerk normally).
3) Kamikakushi Village Murder Case (Vol. 3-4) - I believe this case might somehow be better in the anime. I checked it out and the atmosphere is on-point. And this case might be the most talked about TGQ case due to that fact; the atmosphere. In the manga format I immediately saw the trick that was pulled in volume 3 when the case started, and this case is way too long to really be this high in my list (it's like 13 chapters long), but after watching the anime version I kind of see where people are coming from. The anime is actually really low quality production normally (don't suggest people to watch it), but for this case I really liked what they did as the derpy faces and stuff like that weren't present that much at all.
Especially for those who don't figure the trick out (as it's a grand-scale misdirection type), it's a very atmospheric story.
4) Mystery of the Old School Building (ending and beginning of vol 6-7) - Not really a case "worth mentioning" as I don't think there's anything for the reader to solve, but it's a nice addition to the actual story and has some tensity and mystery towards the future; who was locked up? did they kill the people who locked them up? why was this jail cell created?
5) Murder Collector Case (Volume 7-8) - I personally didn't really like this one as it didn't do much, but I do acknowledge that it's a properly crafted case that's enhanced with a creepy background: an unknown guy in some school collecting snuff videos. But it was kind of stretched and uninteresting otherwise. I hold this case at about the same level as the third entrance exam case (Vol. 2-3) which I believe is a better representation of TGQ as a series.
