Strether sees a boat coming around the bend in the river, and he is surprised to discover that the two occupants are Madame de Vionnet and Chad. He is horrified to realize that "they would show nothing if they could feel sure he hadn't made them out." Deciding that there is only one course of action open to him, Strether calls out with "surprise and joy," and they respond by turning the boat to shore. They have dinner together and return to Paris on the same train. The couple's discomfiture forces Strether to the truth that Madame de Vionnet is Chad's mistress: "Her shawl and Chad's overcoat and her other garments, and his, those they had each worn the day before, were at the place, best known to themselves — a quiet retreat enough, no doubt — at which they had been spending the twenty-four hours." Strether is disillusioned as much with Chad as he is to learn of the affair; Chad, he acknowledges, "habitually left things to others, as Strether was so well aware, and it in fact came over our friend in these meditations that there had been as yet no such vivid illustration of his famous knowing how to live." In the quiet of his room, Strether thinks of his next visit with Maria Gostrey with some apprehension. He almost feels embarrassed by his blindness. Thinking how he would respond to Maria's inevitable question ("What on earth — that's what I want to know now — had you then supposed?"), Strether "recognized at last that he had really been trying all along to suppose nothing."
This chapter can be regarded not only as the climax of the second half of the story (Books VI-XII) but as the climax of the entire novel. Strether's realization now puts him in possession of everything that he must know in order to come to terms with the situation. Whatever his course of action now, it will be based on a full knowledge of the facts and will reflect what Strether is, and has come to be, as a person. Most important will be Strether's attempt to reconcile Bilham's phrase "virtuous attachment" with what Strether now knows to be a relationship that is, in the view of Woollett at least, an immoral alliance.