In the year 1199, Robin Longstride (Russell Crowe) serves as a common archer in the army of King Richard the Lionheart (Danny Huston). A veteran of Richard’s crusade, he now takes part in the siege of Chalus Castle. Disillusioned and war-weary, he gives a frank but unflattering appraisal of the King’s conduct when the King asks his opinion, and Robin and his comrades—archers Allan A’Dayle (Alan Doyle) and Will Scarlett (Scott Grimes) and soldier Little John (Kevin Durand)—find themselves in the stocks.
When the King is slain during an attack on the castle, Robin and his men decide to free themselves and desert. They come across an ambush of the English royal guard by Godfrey (Mark Strong), an English knight who has conspired with King Philip of France to assassinate King Richard. After chasing Godfrey away, Robin decides to take advantage of the situation by having his men impersonate the dead English knights to return to England. Before they depart to sail across the Channel, Robin promises one of the dying knights, Sir Robert Locksley (Douglas Hodge), to return his sword to his father in Nottingham.
Awaking to find his party in the Thames estuary, Robin must continue to assume the identity of Locksley to inform the royal family of King Richard’s death. He witnesses the coronation of King John (Oscar Isaac), who orders the collection of harsh new taxes and dispatches Godfrey to the North to do so—unaware that Godfrey will instead use French troops to stir up unrest and to prepare for King Philip to invade England.
Robin and his companions head to Nottingham, where Locksley’s elderly and blind father, Sir Walter (Max von Sydow), asks him to continue impersonating his son to prevent the Crown from seizing the Locksley family lands. Locksley’s widow, Lady Marian (Cate Blanchett), is initially cold toward Robin, but warms to him when he and his men merrily recover tithed grain for the townsfolk to plant.
Godfrey’s actions incite the northern barons, who march to meet King John. Speaking now for Sir Walter, Robin proposes that King John agree to a charter of rights to ensure the rights of every Englishman and to unite his country. Having realized Godfrey’s deception, and knowing he must meet the French invasion with an army, the King agrees. Meanwhile, French marauders plunder Nottingham. Robin and the northern barons arrive to stop Godfrey’s men, but not before Godfrey has slain the blind Sir Walter.