Set in the 1960s at the height of the pirate radio station craze, a pirate station and a navy sub sailing off the coast of Scotland are the first to suffer at the hands of an alien invasion by telepathic, carnivorous plants (the Grandfathers) and their tall, rocky assistants (the Ymir).
The survivors of both vessels find themselves on the ocean floor, surrounded by an air-sealed protective bubble, and are soon captured by the Ymir and put to slave labour, working to help the invaders enact their dastardly plan: to detonate a bomb in an undergound oilfield that will release millions of tons of carbon dioxide into the earth's atmosphere. With the resultant global warming killing off the pesky humans and most other life, there will be plenty of room for the grandfathers and their cronies to take over. So far, so good.
Lethbridge-Stewart and his team are soon alerted to the strange goings on in Scotland, however, and make their way up North to investigate and put a stop to the Grandfather's ambitions.
After a failed attempt by the RAF to firebomb the infected island, a team led by L-S set out to be captured by the alien invaders disguised as 'ordinary' island folk (concealing as much weaponry as their outfits can hold). Meanwhile, L-S's colleague Ann Travers, is tasked with conducting an investigation using a bathysphere deep sea vessel.
Written by John Peel (no, not him), there are plenty of 60s references, as one would expect, and the Brigadier is his usual gallant / stuff-upper-lipped / get-the-job-done / no-nonsense self. Also, the enemy is one that has been well thought through, despite the obvious inspiration from Wyndham's original story.
In conclusion, the Grandfather Infestation is another excellent addition to the Lethbridge-Stewart series and well worth checking out.