'The Vignes family of France, famous for making premium cheeses, have long been friends with the Doctor; however, he now visits Mathilde Vignes with a policewoman, Inspector Toprak, and accuses her of stealing dangerous bacterial cultures from her younger sister, Victoire. Victoire has been working in pure research and development, modelling and developing new strains of bacteria; twenty years ago, she used her knowledge and experience to help the Doctor defeat an invasion by the Voltranons. The Doctor assured Mathilde at the time that her everyday work in making cheese was just as important as Victoire's work in saving the human race, but Mathilde still feels insignificant in the grand scheme of things and has turned her resentment against her sister. Toprak searches Mathilde's laboratories, and, unable to find any trace of the stolen cultures, begins to take samples of the recently cured cheeses, leaving marks that will decrease the cheeses' value in the marketplace. Mathilde still refuses to admit to the theft, even when the Doctor admits that the cultures would have died within days of leaving the laboratory; he's really interested in the data that was stolen from Victoire's computers. Toprak tires of the Doctor's attempts to reason with Mathilde and pulls out a gun, admitting that she is in fact an agent of the Voltranons; they have been monitoring Victoire's work since she helped to defeat them, and intend to turn her own discoveries against her, using her bacteria to destroy the human race. However, the Doctor has just been waiting for Toprak to reveal her true allegiances, and Chris Cwej now emerges from hiding and overpowers her. Mathilde admits that she stole her sister's work in order to create new moulds of cheese that were resistant to spoilage and infection, and the sisters, reconciled, begin discussing ways to work together and turn Victoire's research to Mathilde's advantage.'
[The Doctor is the Seventh Doctor.]
Source: drwhoguide.com (http://www.drwhoguide.com/whotrip13.htm).Sighted 20/5/11