After the Battle of Waterloo, Joseph, a soldier in the Duke of Wellington's army, returns to his hometown of Manchester, ready to reunite with his close-knit working-class family headed by his parents, Joshua and Nellie. The family, which includes his brother Robert, sister Mary, and sister-in-law Esther, struggles to make ends meet by working in a cotton mill. However, an economic downturn makes it increasingly difficult for Joseph, who is deeply traumatized by his experiences, to find employment, putting their livelihoods in jeopardy.
The family becomes sympathetic to the growing movements advocating for the equal civil and political rights of all individuals and opposing the Corn Laws that prevent them from purchasing cheaper imported grain. Quickly becoming involved, Joshua, Joseph, and Robert regularly attend local political gatherings, where activists such as John Knight, Samuel Bamford, and John Bagguley passionately voice their opposition to a government that only represents the upper class and aristocracy. Meanwhile, Nellie participates in meetings with the Manchester Female Reform Society to rally for women's rights.
The local authorities, commanded by magistrates like Colonel Fletcher, Reverend William Robert Hay, Reverend Charles Ethelston, and Mr. Norris, closely monitor the political climate, waiting to find any pretext to arrest the movement's leaders. With Lord Sidmouth, the Home Secretary, adamant about quelling what he refers to as 'radical' politics, a seemingly inconsequential act by a disgruntled Londoner—smashing the Prince Regent's coach window—becomes the catalyst for suspending habeas corpus.
As the atmosphere thickens, activists Bamford and Joseph Healey journey to London to hear the renowned speaker, Henry Hunt, deliver a political address. Known for his vanity, Hunt's reputation precedes him; nevertheless, Bamford persuades Manchester businessman Joseph Johnson to invite Hunt to illuminate the masses at St Peter's Fields. Unbeknownst to them, the Home Office intercepts this invitation, signaling trouble ahead.
Upon arriving in Manchester, Hunt takes refuge in Johnson's house. However, trouble brews as a Home Office spy, Richards, incites fellow activists like Bagguley and Drummond to openly call for armed rebellion, leading to their arrest. The magistrates hastily prepare to break up the anticipated meeting using the local mounted militia, the Manchester and Salford Yeomanry, and a regular army detachment helmed by General John Byng. Hunt, confident in his ability to lead a peaceful rally, disregards Bamford’s warnings regarding the imminent threat from authorities.
On the day of the assembly, thousands converge upon Manchester, including Nellie and Joshua, eager to hear Hunt's message. Bamford initially leads a procession from Middleton but storms off in anger upon realizing that only Hunt has been allotted the opportunity to speak. A specially convened committee of magistrates, presided over by Mr. Hulton, watches the crowd from an upstairs room, poised to act. Despite Norris's appeals for restraint, Byng delegates control to his deputy as he departs for a horse race.
As Hunt begins his speech, Reverend Ethelston orders the crowd to disperse and reads the Riot Act. However, the assembled masses remain firm in their stance, prompting the Yeomanry cavalry to charge, sabres unsheathed. In the ensuing chaos, Hunt and Johnson are apprehended, while the crowd faces brutal treatment from the militia and army, resulting in multiple fatalities and numerous injuries. Joseph suffers a sabre wound that ultimately claims his life.
The news reporters swiftly return to their offices to shed light on the horrific incident, coining it "The Massacre of Peterloo." In stark contrast to the tragedy, the Prince Regent extends his congratulations to the magistrates for what he views as a successful suppression of 'radicalism' and restoration of "tranquility."
