In chapter 17 of Dark Isle, the main character, Morag, and her friends, Eilidh and Adam, are on a mission to find the missing children of the island. They discover that the children have been taken by the evil witch, Morna, who plans to use them for her own dark purposes.

In chapter 18, Morag and her friends come up with a plan to rescue the children. They enlist the help of the island’s magical creatures, including a selkie and a kelpie, to distract Morna while they sneak into her lair.

In chapter 19, Morag and her friends successfully rescue the children and defeat Morna. However, they soon realize that their victory may have come at a cost, as Morag’s powers have been weakened and she may not be able to protect the island from future threats.

In chapter 20, Morag and her friends reflect on their adventure and the lessons they have learned about the importance of friendship, bravery, and standing up to evil. They also vow to continue to protect their island and its inhabitants, no matter what challenges may come their way.