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
We follow the Bates family on what initially appears to be a fairly typical evening. Basically, Elizabeth Bates and her two children, Annie and John, are waiting for Walter (the family patriarch) to get home. He is late—which isn't unusual.
Act II
Elizabeth and the kids go ahead with dinner in Walter's absence. Elizabeth is annoyed that he's not there; she assumes he's out at the pub boozing, and she says as much to the kids. Annie is pretty anxious about her father's absence. Elizabeth claims not to be, but after she puts the kids to bed, she goes out looking for him—but she has no luck. However, a neighbor offers to go look around some more. Elizabeth goes home to wait.
A little while after Elizabeth returns home, her mother-in-law turns up. It seems that Mr. Rigley, the neighbor who had offered to go looking for Walter, had come by the MIL's house to let her know Walter had had an accident. He had asked her to go sit with Elizabeth. Then, another man arrives and announces that Walter died in an accident at the mine.
Act III
Three men (the doctor, the pit manager, and another collier) bring Walter's body to the Bateses' house to lay him out there. Elizabeth and her mother-in-law then strip, wash, and re-clothe the body. All the while, Elizabeth is contemplating her life with Walter and the ramifications this event will have for her future.