So David takes Tally to his parents' cabin, which is outside of the Smoke.
David calls his parents "mom" and "dad," which is so weird. (Remember that Tally calls her parents by their names.)
Also, weirdly, David looks like his parents. In the city, all those bizarre family traits get removed—like, no one has really big ears or a big nose or frizzy hair or tattoos. (No, wait, tattoos aren't inheritable. Except maybe the desire to get them.)
David's parents Maddy and Az are doctors who have a secret. And they're a little annoyed at David because he brought Tally here and they don't like to tell their secret.
But they will tell her all about… well, that's in the next chapter. Geez, this book is all cliffhangers. Kind of annoying when the chapter titled "The Secret" doesn't even tell us all the big secrets we want to know about.