Black cloud drifts into the solar system and obscures the sun, causing havoc on earth. Astronomers realise its an intelligence and feed signals between it an a human. I think they lose the first volunteer to madness, the second keeps going long enough to explain the damage that the cloud is doing, so it goes away. Then that bloke goes mad, but after he had explained his survival technique. He compared it to the early meetings between Europeans and Tasmanians, which caused the Tasmanians to die of despaire because they couldn't understand the European culture. So if there was a clash between what he believed and what the black cloud said always believe the cloud. His colleagues thought that he hit something so fundamental that he could not adjust to it.

I haven't read Hoyle for 40 years, must try getting hold of some.