In the series premiere, a group of five smart sixth-grade friends—Minh, Son, Sang, Quang, and Tung—embark on their first investigation when their classmate, Sinh, is robbed of 200,000 VND by a teenager armed with a screwdriver. Naming their mission "Operation TTL200", the boys use clever deductive skills, analyzing tire tracks and footprints to identify the culprit's pink bicycle and his physical limp. Their search leads them to Hai, a troubled school dropout living in a local slum with an alcoholic father
In the second episode, the C21 Special Task Force takes on a major case when a daring daytime burglary occurs at three apartments in the E2 residential block. While the adults and local police handle the official procedures, the resourceful group of young friends—Minh, Son, Sang, Quang, and Tung—decides to launch their own secret investigation. By bravely inspecting the roof hatch at the crime scene, they discover crucial physical evidence left behind by the culprits, including Vinataba cigarette butts, a leather camera strap, cut nylon strings, and a large black button from a NATO jacket
In the third episode, the C21 Special Task Force celebrates a major victory as the local police officially arrest the dangerous E2 burglar, earning the young detectives a well-deserved commendation. However, their excitement is quickly interrupted when they find a mysterious anonymous letter in their secret mailbox, written by an unknown person challenging the group to uncover their identity for a chance to join the team. While trying to deduce the author's identity through handwriting analysis, the kids inadvertently uncover and resolve a cheating incident in their physics class
the C21 Special Task Force successfully wraps up their investigation into the school's missing lightbulbs. Through a clever sting operation and a hidden cassette recorder, the young detectives bravely confront "Bóp", the mastermind behind the shady lightbulb exchange scheme. Meanwhile, not to be outdone, the girls in their class—Tuyet and Hanh—prove their own sharp observational skills by noticing a suspicious man and catching a daytime burglar in the act at a friend's house.
n the series finale, the C21 Special Task Force takes on their final summer adventures, starting with a charity drive to collect old books and stories for underprivileged students. During this drive, they discover that a Kama 10 water pump belonging to a disabled war veteran has been stolen and sold to a local scrap dealer. Using a clever sting operation disguised as a fake birthday party for a younger neighborhood boy, the young detectives secretly take photos to identify the culprits. True to their compassionate nature, they choose to recover the pump and educate the young thieves and their parents rather than reporting them to the authorities
