In June 1920, twenty-five-year-old Samantha Parkington delivers a speech at the Mount Bedford Public Library encouraging women to register and vote. Women in New York State won the right to vote three years earlier, but turnout has been disappointing. Samantha connects suffrage to causes she cares about: child labor, orphaned children, better schools, and protections for working women. Her Aunt Cornelia, a longtime suffragist married to Samantha's Uncle Gard, offers encouragement.
Samantha has returned to Mount Bedford for the summer to care for her grandmother, Grandmary, who raised her after her parents died in a boating accident when Samantha was five. Gard, Cornelia, and their son William are departing for a four-month tour of the Far East. Samantha's fall plans include work for the League of Women Voters, an organization dedicated to voter education, and an application to Teachers College at Columbia University to study progressive education.
The summer settles into a comfortable rhythm until late July, when Samantha finds Grandmary in the garden in her dressing gown, confused, addressing Samantha as Lydia, her deceased daughter. Earlier lapses had been easy to dismiss, but Grandmary looked at Samantha and saw someone else entirely.
In early August, someone lures Samantha away with a phone call claiming there is a problem with Grandmary's bank account. The bank manager confirms no call was placed. Returning home, Samantha finds Grandmary in the parlor, frantically searching for papers and talking about men in suits who claimed to be lawyers. Grandmary mistakes Samantha for Lydia, insisting she told her daughter about making the right decision. Over the following days, Grandmary weakens and refuses medical attention. One evening, Samantha tells Grandmary she loves her, words neither has spoken aloud before, and Grandmary returns the declaration. Grandmary's final words urge Samantha to hold on to her convictions and let her actions speak louder than words. The next morning, Samantha learns Grandmary has died in her sleep.
Samantha manages the funeral largely alone. Agatha Pitt, Cornelia's younger sister and an aspiring actress, arrives from Chicago for the service. Grandmary's attorney, Mr. Quigley, reveals that a second will has been filed by a New York City firm, Crowley, Crouch & Timmerman, leaving the entire estate to an entity called MRB Corporation and disinheriting Samantha and Gard. Samantha recognizes MRB as Grandmary's initials: Mary Rose Beemis. The will is dated August sixth, the day the phony call lured her away. Mr. Quigley will contest it in probate court, which handles estate disputes, but the process will take months, and without medical proof of Grandmary's incapacity, the case is weak. The estate is frozen, cutting off Samantha's allowance.
Refusing to wait, Samantha travels to New York City. The lawyer Eugene Crouch refuses to see her and rushes out, telling his receptionist he will meet a Mr. Malloy at Sunny Beaumont's. Gard and Cornelia's Gramercy Park townhouse is occupied by family friends, so Samantha makes her way to Agatha's boardinghouse, Hummingbird House, arriving stranded and nearly broke. Agatha helps her secure a room and a job at B. Altman & Company department store.
When the Nineteenth Amendment is ratified, Samantha celebrates but remains aware that Black women across the South still face poll taxes, literacy tests, and violence designed to deny them ballot access.
Recognizing Sunny Beaumont's as the venue Crouch mentioned, Samantha accompanies Agatha to the cabaret. She spots Crouch at a table with two men and engineers a collision with the younger one, Tommy Quinn, one of Malloy's employees, to gain access. She learns Crouch is the personal attorney of Leonard Malloy, a shipping magnate who runs gambling dens and is exploiting Prohibition. Samantha realizes Malloy is behind the fraudulent will. While working at B. Altman, she also acquires a signed slip bearing Crouch's distinctive handwriting, which she keeps.
Two relationships develop. Richard Strickland, an acquaintance from Mount Bedford working for an anticorruption commission led by former Judge Clifford Hanley, promises to bring Samantha's case to the judge. He courts Samantha and proposes in Central Park, but she declines, wanting a master's degree and a teaching career. Meanwhile, Samantha and Tommy discover common ground as orphans with ambitious dreams: He envisions a future in airplane shipping, and she wants to transform how children learn.
After being fired from B. Altman, Samantha takes a clerk position at Malloy Shipping Company, hoping to find evidence linking Malloy to Grandmary's estate. She overhears plans for a whisky shipment from Scotland. When she visits Judge Hanley on her own, she discovers Richard never told the judge about the will.
Alone one evening, Samantha opens a locked drawer in her supervisor's desk and finds cash and a payment ledger. In Malloy's wastebasket, she discovers torn fragments of a note from Crouch confirming that Grandmary signed the will without understanding what she was doing, and that Samantha was deliberately lured away.
The whisky drop is moved without Richard's knowledge, and the Commission's raid fails. Richard bursts into Malloy's office, inadvertently exposing his role as Malloy's mole inside the Commission and his connection to Samantha. Malloy orders them to the basement. There, Richard confesses: Drowning in gambling debts from Malloy's dens, he conspired with his Uncle Milton Strickland to steal the estate after Milton learned of Grandmary's mental decline. Richard was one of the men who visited the house on August sixth.
Tommy secretly loosens Samantha's bindings. She hides a hoof pick, a tool for cleaning horse hooves, found during a bathroom trip. When Malloy's enforcer Paddy brings them to a loading dock, Samantha frees her hands and strikes him with the pick. Tommy removes her gag, and they flee into the night.
Tommy brings Samantha to Judge Hanley's townhouse, revealing that he has been the judge's informant inside Malloy's organization for the past year, motivated by his dying mother's plea to break free. Samantha presents the torn note and the signed slip from B. Altman, proving the handwriting matches Crouch's. The judge secures a search warrant.
Searches yield extensive evidence. Malloy and Paddy are killed fleeing; Crouch is found dead. Gard and Cornelia return home. Gard drives Tommy to Piney Point, the family's Adirondack lodge, to catch a northbound train to Canada as a protected witness. There, Samantha and Tommy discover old letters from Milton to Samantha's mother, revealing decades of resentment at being spurned. At the dock, they confess their feelings and share a kiss.
Walking back, Milton and Richard ambush them at gunpoint. Milton reveals that his obsession with Lydia fueled the estate scheme. Samantha connects this to Grandmary's confused words about telling Lydia she was making the right decision: Grandmary had recognized the Stricklands. In the ensuing struggle, the gun fires accidentally, killing Milton. Gard, who followed through the woods, tackles Richard.
Richard is arrested; Tommy departs for Canada. Samantha moves into Gard and Cornelia's townhouse. Agatha's Broadway debut in
Heartbreak House opens to rave reviews. Mr. Quigley confirms the second will is invalid, and Grandmary's estate will be distributed as originally intended. Samantha plans to use her inheritance for a master's degree at Teachers College and a donation to the League of Women Voters on Grandmary's behalf.
On Election Day in November 1920, Samantha casts her ballot alongside her family. She and Tommy have been exchanging letters from Canada. Standing with those she loves, Samantha vows to live a courageous life in honor of Grandmary and the women who came before her, declaring this not the end of her story but the beginning.