The Grandfather Infestation (novel)

 was the seventh novel in the Lethbridge-Stewart series. It was the first of the series to feature Alistair Lethbridge-Stewart as a brigadier and not a colonel. Additionnally, it was the first to feature the Home-Army Fifth Operational Corps, which was a British military organisation led by Lethbridge-Stewart and investigated alien actions.

Publisher's summary
The late 1960s and pirate radio is at its height.

DJ Mary Wilde is second-guessing herself, and her career choice - is she a fool to think she can succeed in a man's world? But such problems are soon put into sharp relief when something emerges from the depths of the North Sea, and drops Radio Crossbones down.

Meanwhile, Brigadier Lethbridge Stewart has to contend with the politics of running the Home-Army Fifth Operational Corps, but he's soon pulled away from such tedious back-patting when a nuclear submarine is lost with all hands while investigating the strange occurrences in the North Sea.

What are the Ymir, and why is it important for them to collect so many humans for their Grandfathers? And why does their success spell certain doom for Edinburgh? Lethbridge-Stewart, Anne Travers and Mary Wilde are about to learn the shocking truth first hand.

Characters
to be added

Continuity

 * DN6 pesticide is used on the island of Strommach. (TV: Planet of Giants)