The King's guard Legrand arrives with a vital mission for Robin. As Robin joins the quest to unravel the coded clues leading to the mysterious Thesaurus Patriae, Marian decides to act alone in helping Locksley villagers, only for Gisborne to finally unmask her as the Nightwatchman. The Sheriff is hunting the Thesaurus Patriae, too. Everyone's in for a surprise when King Richard's treasure turns out to be neither gold nor jewellery.