So now, Percy's mother wants Adela to fall in love with Percy, but she is worried that Adela is going to fall in love with Dr. Armstrong (Harry) instead.  So she goes to the Colonel and tries to insinuate that there is some kind of relationship starting with Adela and the young doctor.  

John is in the room and hears this.  He is actually hoping a relationship will start but knows the idea would be too startling to the Colonel at this early stage.  As soon as Percy's mother leaves the room, he makes light of her dire predictions and puts the Colonel back at ease.