A 36-year-old woman is brought to the psychiatrist by her husband because for the past 8 months she has refused to go out of the house, believ- ing that the neighbors are trying to harm her. She is afraid that if they see her they will hurt her, and she finds many small bits of evidence to support this. This evidence includes the neighbors’ leaving their garbage cans out on the street to try to trip her, parking their cars in their driveways so they can hide behind them and spy on her, and walking by her house to try to get a look into where she is hiding. She states that her mood is fine and would be “bet- ter if they would leave me alone.” She denies hearing the neighbors or any- one else talk to her, but is sure that they are out to “cause her death and mayhem.” Which of the following is the most likely diagnosis?