The film opens with young Kate Barker, portrayed by Lisa Jill, experiencing brutality from her family, including her father and older brothers. Fast forward 35 years, we meet the adult Kate 'Ma' Barker, played by Shelley Winters, who no longer plays the victim; instead, she leads a life of crime, committing robberies with her four sons. Among them are the practical Arthur (Clint Kimbrough), the cruel Herman (Don Stroud), the openly bisexual Fred (Robert Walden), and the drug-dependent Lloyd (Robert De Niro).
Set in the late 1920s, Ma abandons her husband, George, and leaves their Arkansas home. With her sons in tow, she embarks on a deadly crime spree to secure a fortune, always keeping her boys under her iron grip. As circumstances escalate, when Herman and Fred find themselves behind bars for minor theft, Ma seizes control of the gang, plotting a series of bank heists to raise enough funds to spring them from incarceration.
Throughout her chaotic journey, Ma recruits a gunman named Kevin, played by Bruce Dern, who is not only Fred's cellmate but also a rumored lover. They also bring on board a local sex worker, Mona Gibson, portrayed by Diane Varsi, further intertwining their criminal endeavors with personal connections. As the crime wave grows more violent, tragedy strikes when Lloyd commits a horrific act against a young woman by the lake, leading the family to hold her captive. In a shocking display of brutality, Ma drowns her, ignoring the pleas of her sons.
Their misdeeds lead them to Tennessee, where they kidnap affluent businessman Sam Pendlebury, brought to life by Pat Hingle, echoing true events involving a brewery owner named William Hamm. As they demand a whopping $300,000 ransom, the dynamic shifts as Herman begins to form a bond with their captive, resonating with a father figure he never had. However, when Herman and Mona make a daring move to collect the ransom, they encounter FBI agents and barely manage to escape. Faced with reduced ransom demands, Ma orders the execution of Sam, but her sons are unable to commit such an act and instead, release him, deceitfully claiming they followed her orders.
The story reaches a poignant moment when they take refuge in the Florida Everglades. Here, tragedy befalls them again as Lloyd succumbs to a heroin overdose and Mona departs, revealing her pregnancy and the risks of staying with the gang. Their luck turns dire when they are discovered by local caretaker Moses, who, after witnessing a reckless act, tips off the authorities.
The climax escalates into a fierce shootout as the FBI and local police converge on the Barker family's hideout. Chaos ensues, leading to the demise of Kevin, Fred, Arthur, and Herman in graphic confrontations. Ma stands as the final barrier, facing her tragic end amidst the fallout of her violent reign. In a gripping conclusion, the legacy of the Barker gang collapses under the weight of their own transgressions.
