In the late 18th century, young idealistic barrister William Garrow is given his first criminal defence case at the Old Bailey by attorney and mentor John Southouse. He defends Peter Pace, who is accused by renowned thief-taker Edward Forrester of robbing a man at gunpoint. The case is won by Garrow's nemesis Silvester, but Garrow's impressive performance in court catches the eye of Lady Sarah Hill. She instructs him to defend a helpless serving girl, Elizabeth Jarvis, who stands accused of murdering her newborn baby. Garrow learns a harsh lesson from his first case, and vows to defend the life of Elizabeth.

William Garrow is now a celebrated Old Bailey barrister and, encouraged by Southouse, he defends the case of the infamous Monster, a man who carries out a series of stabbings on young ladies across London. As a result, Garrow's popularity diminishes with the public and the press. However, Renwick Williams, the accused, is described by Garrow as a 'lecherous libertine' and his defence is not easy. Garrow's friendship with Lady Sarah grows closer, a fact which does not go unnoticed by her husband, Sir Arthur.

After more derision from Silvester, Garrow is spurred on to defend Edgar Cole, a man who is accused of raping a servant girl. Garrow controversially wins and the detestable Edgar Cole is acquitted, much to the disappointment of Lady Sarah. She confronts Garrow but Silvester interrupts and senses the intimacy between them. His insinuation offends Garrow and he challenges Silvester to a duel to defend Lady Sarah's honour. Garrow's next case sees him up against his old nemesis, the violent and unscrupulous thief-taker Edward Forrester. Forrester orders petty criminals Tom and Phebe to steal a box of lace from a shop owned by Katharine Stanton. Garrow seeks help from Southouse, but will his close friendship with Lady Sarah cost him his association with his dear mentor?

William Garrow continues to defend the victms of rough justice when he wins the case of a prostitute accused of murdering a client. Garrow and Southouse's association is still strained until a desperate Mary Hamer arrives in Southouse's office, begging for Garrow to defend her husband. Joseph Hamer has been languishing in Newgate Prison without charge for many months after being arrested on suspicion of sedition. Joseph's case is followed closely by the Secretary of State, Viscount Melville, and Sir Arthur Hill, who engineer charges of high treason against him. Lady Sarah admits to a devastated Garrow that they have no future together. After learning of her husband's role in the plot against Joseph Hamer, she intervenes and the trial takes a surprising turn.

When 133 African prisoners are thrown overboard from a slave ship in suspicious circumstances, Garrow challenges the brutal trade that regards slaves as cargo. It is a case that amounts to a declaration of war.

Garrow defends a man accused of sodomy, a capital offence in Georgian England. But Garrow is embroiled in a simmering sexual scandal of his own - Sir Arthur Hill has accused him of adultery with his wife. In representing an accused homosexual, Garrow risks gossip and humiliation. And, it turns out, he must also perpetuate a lie.

Returning from war, weary and wounded, British sailors are treated with contempt and abuse at the Greenwich Hospital. One man bravely exposes the corruption, and finds himself in a Newgate cell. Southouse accuses Garrow of mixed motives as his uses the case to attack The Admiralty - and in particular its Under Secretary, Sir Arthur Hill.

Having failed to save a twelve year old mute boy from the gallows,Garrow enters the civil court to hear Hill's accusation of adultery against him in a deeply depressed mood,despite Sarah's assurances. Silvester,previously his adversary,defends him in the spirit of fair play and does well,demolishing Hill's Admiralty cronies,the prosecution witnesses,whilst Mary,Sarah's loyal maid,refuses to perjure herself. However,it is the dogged and devoted Soutouse who saves the day by bringing in a surprise,last minute witness to expose Hill's hypocrisy.

William ends up risking his reputation as he returns to the Bailey to defend James Hadfield, who is on trial for high treason for trying to eliminate King George III. He continues to enjoy an "irregular" relationship with Lady Sarah Hill and finds himself ostracised and impoverished. Separated from her husband, Sarah learns from Southouse that she has no independent rights of her own.

Garrow is looking for a challenge, so he agrees to defend two Spitalfield weavers accused of destroying silk looms in an act of industrial espionage - a tough case that becomes more difficult when one defendant testifies against his friend, leaving the barrister conflicted. Meanwhile, Southouse is furious with Lady Sarah for trying to get custody of Samuel.

General Thomas Picton, the Governor of Trinidad, is accused of allowing the torture of a young mixed-race girl - and in prosecuting, Garrow is keen to expose the injustice of the colonial system. But he faces a dilemma when Melville offers him a proposition - if he will limit his prosecution, the lord will use his considerable influence to reunite Lady Sarah with her son.

Garrow successfully defends a man falsely accused of murder at a polling day riot. Approached by the victim's daughter Garrow agrees to find and prosecute the real murderer putting himself in grave danger from the man's colleagues and chief magistrate of the constabulary. Lady Sarah seeks documents to discredit Lord Melville and legally regain her son.