Chart Chaopraya

Twenty years ago at Pak Nam Pho, Nakhon Sawan, Chiao Nampho and Plerng Paknam were disciples of the same master and sworn brothers. Both were skilled and patriotic. Plerng entered the police academy, while Chiao maintained a front as a fun-loving, generous playboy and son of Jua Sua Cheng (Tycoon Cheng), a wealthy rice mill owner in Nakhon Sawan. Uninterested in his father's business, Chiao secretly worked as a government spy.
When the political powers shifted, Chiao's mission was cancelled, and he became a scapegoat. Betrayed by corrupt politicians and his supposed best friend, Chai (the son of the head foreman), Chiao was framed as a criminal and forced to flee. Chai poisoned Tycoon Cheng’s mind against his son, gaining the tycoon's trust to manage the business. Chai then embezzled funds, built his own influence, and sent hitmen to kill Chiao and his family.
Chiao fled with his three pregnant wives: Rerai, Kimlang, and Oradee. They all gave birth to four sons on the same day and year near the convergence of the Chao Phraya River. Chiao named them Ping, Wang, Yom, and Nan. Ping was Rerai’s son; Wang and Yom were fraternal twins born to Kimlang; and Nan was Oradee’s son. Tragically, Chiao and all three wives were eventually hunted down and killed by Chai’s men.
Plerng tried to help but was too late. Before dying, Chiao entrusted his four sons to Plerng, asking him to hide their identities to protect them from Chai. While rescuing the four babies, Plerng also found a lost 5-6-year-old half-caste boy—a redhead with a brilliant, eccentric mind—and took him in as well (this boy grew up to be Pitsadan, the long-lost son of Dr. Hope).
Meanwhile, Tycoon Cheng died of a heart attack after Chai lied to him that Chiao had been killed while committing crimes. Chai seized all the assets, forged documents to claim ownership, changed his name to Father Thongchai Cherngpanich, and became a powerful mafia figure in Nakhon Sawan. He eventually expanded his business to Bangkok but left his son Ah-Ong, daughter Aomjai, and henchmen Dech and Jeng to manage affairs in Nakhon Sawan, never abandoning the thought of rooting out Chiao’s remaining lineage.
Plerng advanced in his career to become Police Major Akkanee Pitaksakul. ostensibly retiring early. In reality, he became the head of a secret government organization called NISD (National Intelligent Secret Department), dedicated to suppressing criminals the state couldn't touch directly. Plerng separated the four boys to hide their identities until the time was right.
The four young men—Ping, Wang, Yom, and Nan—converge at a "Fun Festival" event. Ping works as a security guard, Wang sells fruit, Yom sells coffee, and Nan, the handsome heartthrob, sells papaya salad. Simultaneously, NISD agents are tracking Muang Man (or Mikhail Ivanov), a notorious international spy rumored to be in Thailand plotting something. The four brothers get caught up in a clash between the agents and the villains, showing off their fighting skills, though they fail to save the NISD agent.
With his best agent lost, Plerng orders Pitsadan to recruit the four brothers to form a new team of agents to serve the nation and expose Thongchai, thereby avenging their parents.
Meanwhile, Father Thongchai and his children are in conflict with Sia Leng, another influential figure in Nakhon Sawan and Bangkok. Thongchai wants to buy Sia Leng's land, but Sia Leng refuses due to Thongchai's shady background. Sia Leng’s daughter, Wadrawee, recently returned from abroad, worries for her father but is told to focus on managing their hotel. There, she meets Dujdao (Plerng’s daughter), an old high school friend and owner of a boutique, who wants to hold a fashion show at the hotel.
Dech brings Thongchai crucial information he has sought for 20 years: the location of the four surviving babies, identified by their shared birthdate.
Suddenly, Ping, Wang, Yom, and Nan receive SMS messages claiming to have information about their parents. They rush to an abandoned warehouse, only to be ambushed, knocked unconscious, and put into coffins to be buried alive. Dech seals Ping’s coffin with a magical talisman to suppress his immense strength. Just as they are about to die without knowing why, Plerng uses his psychic vision to send Pitsadan to rescue them and bring them to NISD headquarters.
Plerng keeps their past a secret for now but invites them to join NISD to serve the country—and eventually discover the truth about their origins. They agree, excited to leave their ordinary lives behind. Plerng names their mission "Chat Chao Phraya" (Chao Phraya Nation).
The four undergo intense training to enhance their combat skills. For safety, Plerng gives them magical wristbands to hide their locations from Thongchai.
During a mission to monitor Sia Leng, an assassination occurs. The four brothers intervene but fail to save Sia Leng, who is killed by Jeng. However, Nan manages to save Wadrawee.
It is revealed that Muang Man and Thongchai are partners. Thongchai ordered Sia Leng’s death to secure land for a joint project with Muang Man: a missile base. Manmook, a private investigator hired to catch a cheating husband, accidentally records their conversation while hiding under a table. She is hunted but narrowly escapes. Thongchai later encounters Plerng (posing as a retired cop) for the first time in 20 years.
Wadrawee receives a mysterious tip-off and begins investigating her father's death by getting close to Ah-Ong, who is interested in her. Meanwhile, Muang Man plots to capture Dr. Hope, a weapons expert, by using his lost family as bait.
Dr. Hope arrives in Bangkok and is immediately kidnapped by Muang Man's men despite NISD's attempts to intervene. The four brothers are tasked with rescuing him.
Later, Dr. Hope (using the alias "Uncle Somwang") meets Dujdao and Ping. Ping helps him, unaware of his identity. When Dr. Hope is recaptured by Muang Man and Liang, Plerng has to use his supernatural abilities to save Dujdao and erase her memory of the event.
Wadrawee suspects Nan (who is undercover as "Thewa") and tries to expose him, putting herself in danger. NISD rescues her, and Plerng reveals the truth, allowing her to help investigate by pretending to get engaged to Ah-Ong.
The villains force Dr. Hope to build a missile, leading to a race to find Tantalum ore. After several clashes, Ping and Nan are captured but manage to escape.
In the final confrontation, the four brothers, Wadrawee, and Manmook join forces to save Dr. Hope. Pitsadan discovers Dr. Hope is his biological father. Muang Man flees, leaving Thongchai to fight. Ah-Ong is killed, and Aomjai dies in Nan's arms. Thongchai uses dark magic against Plerng but is eventually overpowered by the combined strength of Ping and Nan. Thongchai kills Muang Man to escape via helicopter, but the brothers shoot it down, ending his reign of terror.
With the mission complete, Chiao’s name is cleared, and the government secretly honors the team. The brothers pay respects to their parents at Pak Nam Pho.
In matters of the heart: Yom steps aside to let Wang be with Manmook (as the older twin sacrifices for the younger). Plerng accepts Ping as his son-in-law after seeing him protect Dujdao. Nan reconciles with Wadrawee. Pitsadan plans to stay in Thailand to serve his country. Anna Marie, Dr. Hope's daughter, arrives, and Yom instantly falls for her.
The story ends with three couples engaged and a new romance blossoming for Yom. Plerng then announces a new mission for the "Chat Chao Phraya" team, and though they grumble, they are ready to serve.