Every day Mr. Washington and the two boys go hunting in the woods, or fishing, or playing golf together.
John finds that Mr. Washington is uninterested in any opinions other than his own, and that Mrs. Washington is aloof and indifferent to her two daughters, yet interested in her son, Percy. We learned from Kismine that she is a Spaniard, and she holds lengthy, rapid, unintelligible conversations over dinner with her son in Spanish.
We learn that Jasmine – the third sibling – looks like Kismine (though less perfect) but has a very different temperament. She always wanted to go to Europe to work as a canteen expert during World War I and was disappointed when the conflict ended. She doesn't have quite the same degree of arrogance that Kismine and Percy inherited from their father.
When John expresses his admiration for the landscape, Percy explains that his father captured a landscape gardener, an architect, a designer, and a French poet to design it. They didn't do such a great job, in part because they were being held against their will. He ended up getting a "moving-picture fella" who did a decent job, though (8.6).
As the month of August draws to a close, John regrets that he'll have to leave soon to go back to school. He and Kismine talk about eloping next June.
It's all going great until Kismine accidentally mentions the other guests they've had stay with them for the summer.
It soon comes out that Braddock always murders his children's guests before they can leave the estate – to make sure that the secret of his diamond mountain is never revealed.
Naturally, John is horrified at his impending death. But Kismine thinks that "it's only natural" that she and her family "get all the pleasure out of [their guests] that they can" before they are murdered (8.33).
Anyway it's never been a problem, she says – father always does it before she or Jasmine or Percy know it's time, that way they never have to deal with any tearful good-byes or anything. Apparently he just poisons the guests in their sleep. Besides, she says, she doesn't want to see John die, but she would rather have him murdered than ever kiss another girl.
She laments that she told John all of this, because now it will spoil their fun for the rest of the summer.
John is furious; he wants nothing more to do with Kismine. But he quickly realizes it is in his best interest to tell her that he still loves her and plan for the two of them to run away together. They do just that.