In 15th century England, Lord DeVere (John Rodion) is executed for treason by King Edward IV (Ian Hunter). John Wyatt's (John Sutton) loyalty to his cousin and refusal to enter into a planned marriage to strengthen royal ties angers Edward and his younger brother, Richard, Duke of Gloucester (Basil Rathbone), resulting in Wyatt being imprisoned in the Tower. Edward and Richard hope to kill the aging King Henry VI (Miles Mander) during the Battle of Tewkesbury, but he survives and is murdered by Mord (Boris Karloff), an executioner and Richard's ally. After winning the battle and killing the Prince of Wales, Richard sets his sights on Anne Neville (Rose Hobart), the Prince's widow. However, Clarence (Vincent Price), brother of Edward and Richard, tries to prevent this by arranging for Anne to be hidden away. Mord's spies eventually locate her and she is tricked into marrying Richard. Soon after, Richard drowns Clarence in a large wine barrel.
After King Edward dies, his eldest son, Prince Edward (Ronald Sinclair), is crowned king. On Richard's orders, Mord murders the boy king and his brother in the Tower. Now king of England, Richard tries to prevent the stolen royal treasure from reaching Tudor in France, but Wyatt transports the treasure to the exiled king. With a new army, Tudor returns to England and meets Richard and Mord at the Battle of Bosworth. Richard and Mord are killed in battle and Tudor is declared king.