4x22 - The Adventures of Robin Hood

Will Scarlet witnesses the murder of an envoy. He and Robin capture Wilfred who had led the envoy into the trap. They discover that the killer was Sir Hartley who intends to kill Constance, Duchess of Brittany, who is taking the King's son, Prince Arthur, to Northumberland to be received as the rightful heir to the throne. Fearing trouble from Prince John, she wants Robin and his men to escort them.