For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
In Act I, the narrator moves from animal loving, happily married man, to hard drinking, cat killing, violent man. As the curtains close, we watch the man, his wife, and one member of the household staff stand outside the burning house.
Act II
Act II opens on the slightly raised image "of a gigantic cat" on the wall of the man's old bedroom, the only wall that didn't burn. Soon after, the man meets another cat, surprisingly like Pluto. The man moves from mild dislike of the animal, to intense disgust. When he tries to axe the cat, his wife stops him. The curtains close on Act II as the man splits her skull with the axe.
Act III
Act III opens on the man bricking his wife's body up in the wall. The man has four days of relative peace after this – the cat seems to have disappeared, finally. In this act, we watch the investigation into the woman's disappearance. The curtains close after the brick wall is torn down, and the cat is discovered, along with the body of the man's wife, there in the tomb.