Detective Academy Q is the story of a group of young students from Class Q of Dan Detective Academy (DDS), a prestigious and renowned detective academy founded by Morihiko Dan, the most famous detective in Japan, and the adventures and mysteries they unfold and solve together. They eventually work against Pluto, a mysterious organization which creates almost fool-proof plans that only a handful of detectives can solve.

                Classes in DDS are based on the entrance test score, with A as the highest, B as the next lower, etc. It is possible for a student to be transferred to a higher class or vice versa, depending on their academic performances. However, Class Q is a special case. As the name might suggest, Class Q is for the Qualified students (i.e the specially chosen few) who are viewed as the most potential candidates for the successor of Morihiko Dan in the future. Yet, the same rules as the other classes also apply to Class Q. Any member of Class Q may be transferred to a lower class if his/her academic performance declines. Since Class A was generally regarded as the top class of the DDS before Class Q was formed, there has been a tense rivalry between the two classes since.

* Age: 14
* Height: 161cm
* Weight: 53kg
* Blood Type: O

                A bright, sweet and optimistic boy who is also a brilliant detective, but a little awkward in social situations. Otherwise, he is considered to be the team's leader and is known for his logical explanations of cases.His motto(taught by Dan himself) - "A Detective must never give up or the case will remain unsolved". He has a good sense of judgement regarding to people (when everyone distrusted Ryu, he expressed his open appreciation for him) but often says things that infuriate Megumi. But even though he acts this way, he cares for her, as shown when they where trapped in a secret door in the old school building. He did everything he could to help Megumi as she struggled after getting bitten by a pit viper, even opening up the pipe system to send Ryu and the others an SOS. In addition, another such running gag of Kyu's is his constant misinterpretation of the Japanese language (for example, he said "training pants" when he heard the words "tore han", which means "treasuring hunting").

                Kyu had been a single child of a single parent (his mother) for as long as he could remember. He didn't have a father, but there's a certain man who had been acting as his mentor when he was little. When he was six years old, he was kidnapped and held as a hostage by some criminals, but his mentor rescued him. In reality he was none other than Kyu's father (Satoru Renjou, Morihiko Dan's partner and right-hand man). Realizing the high risk of being a detective, Satoru formerly married Kyu's mother in secret to keep his new family safe. After Renjou's death, Kyu's mother hid the truth from Kyu for years, trying to shield him from the danger that the life of a detective is always in; after he was accepted in the DDS, Mrs. Renjou changed her mind and supported him fully. One of his favourite words after solving the mystery is "There could only be one answer!"

* Age: 14
* Height: 163cm
* Weight: 47kg
* Blood Type: A

                Commonly referred by her friends as just Meg, she has a unique talent of having a photographic memory ("Shunkan kioku" in Japanese), allowing her to memorize a scene instantly. This allows her to notice if a piece of evidence has been moved or is missing. It is believed that she has somewhat of a crush on Ryu. But, throughout we see that she gets somewhat jealous if another girl is with Kyu (As seen in episode 12). She studied in the Tokyo National Talent Development Research Center alongside Yutaka Saburomaru. She lives with her older sister Akane (who attends a local university) as her parent work abroad. She also sometimes blushes while looking at Ryu. But later in the series, she takes a liking to Kyuu.

* Age: 14
* Height: 166cm
* Weight: 50kg
* Blood Type: AB

                Ryu is very intelligent, and his dark background somehow links him to the organization known as Pluto. When his parents died, Pluto took care of him. As a child he was never allowed to socialize with others. He often viewed his house as more of a prison than a home. Even with his cold personality he is still friendly with the other members of Class Q, and shares a special link with Kyu, since he was the first one who could understand him.

* Age: 11
* Height: 142cm
* Weight: 38kg
* Blood Type: B

                Kazuma is a rich, well known computer games programmer. He often helps to find information on his laptop computer, which he carries around with him all the time. At first after learning that he was a member of Class Q (which at the time was believed to be the lowest) he tried to get transferred in Class A. However, when his classmates came to his aid when he was in trouble he changed his mind, preferring to stay with his friends. Kazuma has a friendly rivalry with Kinta due to their different approaches to detective work. Kazuma and Kinta are often the butt of each others jokes. He is a very smart prodigy, but he can't get right answers without his "lucky" hat as implied in episode 3; he seems to get over this flaw by the end of the TV series.

* Age: 18
* Height: 180cm
* Weight: 70kg
* Blood Type: O

                Kinta is the son of a well respected police officer, but moved out due to a family dispute. He now lives alone and works part-time as a mascot on the seafront. Kinta is the strongest member of the class, having had lessons in judo, kendo and karate. He also has superb senses, especially his eyesight and sense of smell. Kinta often mocks Kazuma's high tech approach to detective work, preferring instead to rely on his "instinct". His tough personality as well as his excellent senses have been very useful at times. He is very strong and sometimes hits either Kazuma or Kyu. He also repeatedly tries to pick up girls (with little success).

                Born in 1936, Morihiko Dan is the founder and principal of Dan Detective School, and a famous detective who has solved many cases, and is the only private detective in Japan who is licensed to hold a gun. Morihiko Dan was a former police officer who resigned to open up a private detective company of his own, Dan Detective Company (DDC), the parent company of DDS. He was assisted by a young boy named Satoru Renjo, who acted as his partner, assistant, and apprentice. Together they helped build DDC and DDS into a top level detective company and school (some of the top-level detectives at DDC and instructors at DDS were the first generation students of DDS). Among many criminals they fought, the most powerful one was the crime organization known as Pluto. Although Pluto was finally thought to apparently have been destroyed, it wasn't without cost. Satorou Renjo, Dan's most prominent apprentice and heir-apparent was killed, and Mr. Dan was forced to be in a wheelchair for the rest of his life. Years later, there are signs that Pluto was being resurrected. Realizing that his days were numbered due to his old age, Morihiko Dan decided to open a new, special class called the Class Q, consisting of several extremely talented persons. He would train them, analyze each one of them, and appoint the best student of this class to be his successor.