Because of Mrs. Mallard's heart condition, everyone basically tiptoes around her and treats her carefully. When her sister and family friend discover Mr. Mallard got killed in an accident, they take time to gently tell Mrs. Mallard that her husband has died. Mrs. Mallard cries her eyes out, then goes to her room to be by herself and locks the door.
Inside, she seems terrified of some knowledge that's coming to her and finally realizes that it's her freedom. Even though she and her husband loved each other, and she's truly saddened by his death, she feels liberated and free for the first time. She looks forward to the days ahead instead of dreading them.
While Mrs. Mallard is having this epiphany, her sister keeps trying to check on her. Finally, Mrs. Mallard comes out of her room, newly resolved, and she and her sister start to go downstairs. Suddenly, the very not-dead Mr. Mallard comes in. When Mrs. Mallard sees him, she has a tremendous shock and dies.