The gem holders arrive in Montliskeard Bay for Martha, however one of them, Rob Appleton, goes rogue and agrees to try and help Luke out. Tom and Nell face danger again as they meet a wolf in 'green' clothing.

Tom and Nell find their work smashed and Rob knocked unconscious on the boat. In spite of the previous attack, Nell decides to go diving again so that Luke can be reassured. Meanwhile, up at Montliskeard Place, Barnes falls foul of Martha.

Martha is closer than ever to achieving her evil goal. Rob and Fran attempt to stop her, and are held prisoner. Nell launches a desperate last-ditch bid to rescue Luke from the cave, preventing Martha's ritual from unleashing destruction.