On her 60th birthday housewife Hetty Wainthropp (Patricia Routledge) decides it's time to do something with her life. A forceful character & naturally inquisitive, she has a certain flair for investigative work, so recruits an unlikely partner in Geoffrey Shawcross (Dominic Monaghan), a runaway teenager whom she has rescued from a life of shop-lifting. With an old head on young shoulders, the Wainthropp Detective Agency is open for business!

Hettys normal appearance, strong sense of justice, kindly disposition and skill at blending into her surroundings bring her into contact with people from all sections of the community. So far Hetty has led a rather sheltered life, but her initial navety is outweighed by her commonsense and shrewdness, and streetwise Geoffrey (her new lodger-cum-sidekick) is there to warn her of potential hazards. To begin with money is tight and cases few and far between, but soon Hetty establishes a reputation for getting results even Detective Chief Inspector Adams (John Graham Davies) begins to treat her with respect.

Every private eye has a trademark and Hetty has two: an unending supply of berets and a scooter (Geoffrey driving, Hetty on the back).

Set and filmed on location in the North West of England, with its rundown post-industrialist towns and magnificent countryside, Hetty Wainthropp Investigates is a charming mix of suspense and gentle comedy with a redoubtable and very unusual heroine.