A 41 year old woman working as an Executive Director is convinced that the management has denied her promotion by preparing false repos about her competence and have forged her signature on sensitive documents so as to convict her. She files a complaint in the police station and requests for security. Despite all this she attends to her work and manages the household. She is suffering from:

Lady in the question does not suffer from hallucinations, does not have social dysfunction nor disorganized speech or behavior. Thus does not fulfill the diagnostic criteria for schizophrenia. Hence the most likely diagnosis is persistent delusional disorder. Persistent delusional disorder is a condition in which delusions one last for more than 3 months. It's onset occur usually in middle age. Delusions are usually systematized (stable and combined into a complex system) and are often encapsulated. Rest of mental state may be unremarkable to the point that if the delusional system is not detected, no abnormal features are elicited. Ref: CURRENT Diagnosis and Treatment: Psychiatry, 2nd Edition, Chapter 16 ; Lecture Notes: Psychiatry By Paul Harrison, Chapter 12