How does the author use foreshadowing in A Case of Need?

In Chapter Seven, when John meets Ev Randall, she tells him to go away but he seems to catch her attention by saying that her husband "doesn't quite understand everything." Those words make Mrs. Randall turn off the ignition of the car and pay attention to what John has to say. This foreshadows things to come. John is also interested in the amount of blood on the driver's side of the Randall's car, but again doesn't yet explain why.