In a medium-sized Chinese city in the northeast during the 2000s, near the Russian border, an elderly, overweight man Ding witnesses a stabbing carried out by a gang, yet he hesitates and cannot identify the suspect when the police ask. The investigation quickly uncovers his past as a retired Central Security Bureau officer from Beijing, and authorities suspect he may be suffering from dementia. Back at home, Ding is frequently invited to share meals by his land-lord Park, an elderly woman who finds him appealing, while he quietly cares for a little girl named Cherry, who lives next door.
Cherry’s father, Li Jia Shan, is a gambler whose mounting debts pull him deeper into trouble. When Li is pressured to undertake a crime, Choi, a Chinese man of Korean descent who leads the gang, forces him to steal the shoulder-bag of a Russian gang leader. Li manages a daring escape with the bag, but his debt remains. In a brutal escalation, Li hides with the bag, and Choi orders his men to abduct Li’s daughter to pressure him further. The Russian boss, furious at the violation of his turf, vows retaliation against Choi’s crew.
Choi’s gang tracks Cherry and targets Ding’s home, only to find that Ding is a formidable fighter who repels the assault. To avoid capture, two of Choi’s lieutenants disappear into the countryside. When the police realize Li has vanished, Cherry is sent to stay with her aunt and uncle, but they soon want her out, and Ding agrees to look after her. Then Cherry vanishes again, and Li returns with money to compensate Ding for his services, only to be confronted by Choi’s men outside the house. Li is killed in the ensuing clash, and the shoulder-bag is reclaimed by Choi’s gang.
Driven by years of guilt over the granddaughter who vanished on a hiking trip, Ding resolves to recover Cherry by force. He barges into the gambling house and demands Cherry’s release, and when Choi’s men attack, he single-handedly overpowers roughly twenty of them, including a skilled knife-wielder. Just then, a wave of Russian gang members arrives, killing several of Choi’s associates as they seek to recover the stolen money. Choi escapes, but Ding injures him, while the Russians, mistaking Ding for an ally of Choi, turn their attention on him. Ding fights back, killing the intruders to protect himself.
The chase spills into the streets as the police, led by Park’s son, pursue two leaders of the Russian gang, who die after colliding with a truck. The two henchmen who had been sent to the countryside murder Choi and steal from him after accepting a Russian bribe to betray him. In the aftermath, Ding’s dementia worsens, and the weight of Cherry’s absence crushes him, though the police understand that his actions were acts of self-defense rather than malice.
Then Cherry returns, revealing she simply ran off to stay with a friend. Even as Ding forgets most of his family, he clings to the memory of Cherry and the care she shows him into his senescence. A post-credits moment shows two countryside criminals stumbling into the path of drill-training PLA military police, who give chase and eventually capture the remaining culprits.
