It's 1199 and King Richard the Lionheart (DANNY HUSTON) is plundering his way across France on his way back to England following the crusades. Among those in his army is Robin Longstride (RUSSELL CROWE), a proficient archer, and his small team including Will Scarlet (SCOTT GRIMES) and Allan A'Dayle (ALAN DOYLE).
They're soon joined by fellow soldier Little John (KEVIN DURAND) in the stockade when Robin is asked to freely speak his mind about the King's behavior. When King Richard is struck dead, Robin and his men escape and then come across a group of knights who've been ambushed. Realizing they can fake being knights to assure safe passage back to England, Robin also promises to fulfill a dying man's wish to return a sword to his father.
Before they get there, however, Robin delivers the crown to the late king's mother, Queen Eleanor of Aquitaine (EILEEN ATKINS), all of which means Richard's younger brother, Prince John (OSCAR ISAAC) -- who's planning on divorcing his barren wife in favor of Isabella of Angoulême (LEA SEYDOUX) -- is now king.
John immediately dismisses William Marshal (WILLIAM HURT) from his post and relies solely on his lifelong friend, Godfrey (MARK STRONG), for advice. Little does he know, however, that Godfrey is secretly conspiring with the King of France to turn the Brits against their new ruler so that the French can invade and more easily conquer them.
Unaware of this, Robin continues on his quest to return the fallen knight's sword to Sir Walter Loxley (MAX VON SYDOW) of Nottingham. A blind and elderly baron, he grieves Robin's news about his son, but wants him to pretend to be that man -- who's been gone for more than 10 years in the Crusades -- and thus pose as the husband to Walter's daughter-in-law, Marion Loxley (CATE BLANCHETT).
She's initially against the idea, but realizes she needs him not only in order to save her 5,000 acres should Walter pass away, but also to help her deal with the Church -- locally represented by Friar Tuck (MARK ADDY) -- and the law embodied by the Sheriff of Nottingham (MATTHEW MacFADYEN). As Robin settles into that role, he must also contend with Godfrey's treacherous plan that soon makes its way to both Nottingham and the coastal shores with the arrival of the French navy.