In Belfast, Gerry Conlon finds himself mistakenly identified as an IRA sniper by British security forces, leading to a chaotic pursuit that culminates in a riot. To protect his son, Gerry's father, Giuseppe Conlon, sends him to London in an attempt to deter an IRA response against him.
Gerry's life takes a darker turn one evening when he breaks into a prostitute's flat, stealing £700. While indulging in drugs at a park with his friend Paul Hill, along with homeless Irishman Charlie Burke, a catastrophic explosion rocks Guildford, resulting in the deaths of four off-duty soldiers and a civilian, while injuring many more. Upon his return to Belfast, Gerry finds himself captured by the British Army and the Royal Ulster Constabulary, leading to his arrest on terrorism charges.
Transported to England, Gerry and Paul, alongside two others, become known as the Guildford Four, where they endure brutal torture during police interrogations. Determined to prove his innocence, Gerry ultimately succumbs to pressure, signing a confession after police threats against his father's safety. Unfortunately, Giuseppe and other members of the Conlon family are soon arrested, collectively known as the Maguire Seven. Despite the defense highlighting numerous flaws in the police investigation at trial, Gerry and the Guildford Four receive life sentences.
In prison, Gerry and Giuseppe encounter a new inmate, Joe McAndrew, who reveals that he was actually responsible for the bombing and had confessed this to the authorities. Strangely, this crucial revelation is suppressed to protect the police’s reputation. As time passes, Gerry's initial rapport with Joe deteriorates when Joe commits an act of violence against a despised prison guard during a riot. The tragedy escalates with the death of Giuseppe in custody, prompting Gerry to assume his father's struggle for justice.
Meanwhile, Giuseppe's attorney, Gareth Peirce, diligently investigates the case and uncovers essential evidence that supports Gerry's original alibi, marked by a note stating, "Not to be shown to the defence." This discovery becomes pivotal when a courtroom appeal reveals a statement from Charlie Burke that ultimately clears Gerry and the others of all charges.
The film concludes by highlighting the ongoing plight of those wrongfully accused and the grim reality that the police responsible for the case faced no repercussions. Additionally, it underscores that those truly behind the Guildford Bombing have yet to be held accountable.
