The exposition is the beginning of the story and prepares the way for upcoming events. the exposition of the radio play is when they introduce the setting and Mrs. Stevenson.
The rising action occurs when the main problem or conflict is addressed with a form of action. The rising action was when Mrs. Stevenson wanted to call her husband but he was not answering so she called the operator.
The other rising action was when she finally got a hold of her husband but, instead she hears someone talking about murdering someone. She was wondering if the operator called the wrong number.
The climax is the point in the story when the protagonist deals with the culmination of events. The climax was when Mrs. Stevenson started to freak out and called the police but, they could not help her.
The falling action was when Mrs. Stevenson heard someone in her house and tried to call the police but they were not answering. That was when she also figured out that she would be the victim.
The resolution was when the murderer came in Mrs. Stevenson's room and killed her.