This chapter didn't move the plot forward a great deal (and maybe that's why no comments until now, sometimes it's hard to find a hook for commenting anything beyond 'GREAT STORY!', but you'd feel like a simpleton if you only said that...), but everything is moving in the right direction on all fronts. I almost expected a huge disastrous setback at the end; some gnarly cliffhanger like Pierce discovering the truth about them, making any rescue almost impossible.

Naiya and Kara getting comfortable with each other's affection was sweet; and I loved your narrator's aside about how sexual intimacy had always seemed awkward as long as she was alienated from her own former body; but she never knew why. My mermaid heroine Enomena had had the same issues, although she had been more conscious of her gender dysphoria. She compares her feelings about having sex as a male this way:

There are some things that it feels just too strange to do when you feel like you've totally been given the wrong equipment. Like eating ice cream with chopsticks, which even if it's technically possible just seems weird and wrong. Then when you hungry enough you break down and use your sticks, even when you wish God had given you a spoon. But since my transformation I didn't feel any of that chopstick awkwardness anymore. Only now that I had my spoon I was afraid that I would never find anyone to have ice cream with... (A chemical humans were dumping into the seas had caused a dangerous decline in the merfolk population for a while, so there were adults and tiny children, but very few teens)

Enomena goes on+on about her predicament in this and other chapters, probably too much. Children of Naethari is much better at keeping these kind of passages short and to the point, at integrating exposition into the story and balancing backstory & random asides with real-time events. But when I look for what I can cut to shorten it I'm like a hoarder; I don't want to give any of it up...

The Chinese take-out the girls had made me hungry, which might be what made me include that excerpt. The mobile phones seem like they'll be a great help, if they aren't discovered somehow. And Naiya's atrium or whatever it's called could be a huge addition to her arsenal if she can find her voice; so this chapter has hinted at some huge developments in the next few installments. Thanks for getting this posted, as insanely busy as you are.
~hugs, Veronica
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I'm thinking Natalie needs to become a mermaid somehow, but I think that about everyone...