The Companion Chronicles: Council of War

At the Doctor's request, Sergeant Benton is investigating ghosts and missing people in Kettering, while undercover as a local councillor

And that's how he comes to meet Margery Phipps.

An alien incursion in the town hall leads them on a journey to a terrible future – where Margery discovers how she changed a world, and the life of a whole civilisation hangs in the balance...