Yes, the film is the true story of the wartime exploits of Mary Lindell. If anyone wishes further confirmation I suggest they read the book titled 'Saturday at MI9' by the late Airey Neave, Neave being the first British PoW to escape from Colditz and make a home run!
It was Mary Lindell who arranged the return to Great Britain of Hasler and Sparks, the two survivors of the those who became known as The Cockleshell Heroes.
If your interest is SOE and/or the Resistance in France I suggest acquiring the DVD 'Army of Shadows' which I found to be very slow but very worthwhile and authentic. I consider the finest book on the Maquis to be the book titled 'Maquis' by the late George Millar, it was written and published within weeks of the war ending. Initially it was banned by De Gaulle who wanted only the French to feature as leaders of resistance. However, on reiteration, De Gaulle later demanded that the book be standard reading in all French schools.