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.