Meanwhile, Therru sees the same copy of Arren and follows him to the castle, where he reveals that he is the light within Arren and tells Therru his true name. Therru enters the castle and learns of Sparrowhawk and Tenar's sunrise execution. She finds Arren, guilty and hopeless, and brings hope back to him, calling him by his true name and confiding in him her own true name, Tehanu. They rush to rescue Sparrowhawk and Tenar. Arren confronts Cob, who tries to kill him. He fights back and finally unsheathes his sword, which was sealed with magic. Arren cuts off Cob's staff-holding hand. Unable to use any of his magic powers, Cob rapidly begins to age. He captures Therru and flees to the highest tower of the castle, with Arren in pursuit. Cornering Cob, Arren tries to explain what he learned about life and death from Therru and Sparrowhawk to Cob, but the withering Dark Lord refuses to listen and uses the last of his magic to strangle Therru to death. Instead of dying, she reveals her true form as the Black Dragon, possessing life everlasting. Therru kills Cob with her fire breath and rescues Arren from the collapsing tower.