Sir Robert de Rainault, the Sheriff of Nottingham, uses the stolen silver arrow of Herne the Hunter as bait to lure Robin Hood into a trap. When that attempt fails, with Robin winning an archery tournament and reclaiming the arrow, the devil-worshipping Simon de Belleme comes to the Sheriff with an offer to kill Robin for him, taking Maid Marian as his captive in return.
This second part falls broadly into two halves. The first sees Robin infiltrate Nottingham to compete for and win Herne's arrow. The second sees Robin travel to Belleme's coastal keep to rescue Marian. It's testament to the strength of the episode that each half is fairly different in tone - one fairly light and adventure-based, and the other quite dark and foreboding - yet both fit together remarkably well as a single episode.