In Mr. Snagsby’s house, Mrs. Snagsby’s imagination goes to work. She can see that a change has come over her husband and wonders what he is hiding. Meanwhile, Mr. Snagsby is preoccupied by the mystery he was involved with. He is afraid of Mr. Bucket, who seems to be all knowing, and grows nervous when any unknown person comes into the shop. Mrs. Snagsby’s suspicion makes Mr. Snagsby feel guilty, and this increases her suspicion. She begins to spy on him and to read his letters and other documents at night.
Rather than ask her husband what’s going on, Mrs. Snagsby invents fantastical mysteries in which he may be embroiled. Mr. Snagsby, ironically, is totally oblivious of the real mystery that he has become involved with—the mystery of Lady Dedlock’s secret and Esther’s identity—and imagines that he plays a much greater role in it than he really does.
The next evening, Jo arrives for his lesson from Mr. Chadband. Mrs. Snagsby is convinced that Jo is Mr. Snagsby’s son and watches for signs throughout the evening. Jo is extremely confused by events and seems unsure what Mr. Chadband wants from him. Guster and the other servants gather to watch as Mr. Chadband launches into his sermon. Mrs. Snagsby, who sees signs of Mr. Snagsby’s infidelity everywhere, believes that Mr. Chadband refers to this in his sermon and grows hysterical. Eventually she needs to be carried out of the room, much to Mr. Snagsby’s confusion.
Mrs. Snagsby has convinced herself that Mr. Snagsby has an illegitimate child, and that that child is Jo. Once she gets this idea, she does not reason with herself but thinks that she sees “signs” everywhere that prove her hunch is correct. She becomes so overwrought with this idea that she sends herself into hysterics. Mr. Snagsby, of course, has no idea why she is so upset.
Jo, who has nearly fallen asleep during Mr. Chadband’s lecture, is finally allowed to leave. He meets Guster downstairs, who shares her supper with him and asks Jo about his parents. They are both orphans and know nothing of where they came from. On Jo’s way out of the house, Mr. Snagsby gives him a half-crown, and Mrs. Snagsby watches silently from the stairs.
Mr. Chadband claims that his lecture is designed to help Jo, but really it is just a confusing inconvenience to the boy. Guster relates to Jo, because she is an orphan herself, and is kind to him. Mrs. Snagsby seems increasingly mad as she interprets Mr. Snagsby’s simple kindness to Jo as evidence of her husband’s guilt.