The main character, Elsa, is mentally ill, according to her husband and children. Therapy has been ineffective, and what's worse is that madness seems to be catching: One by one, the other characters realize that Elsa's shadow points in the wrong direction:
And Paul, still standing in the middle of the carpet, then looks at her shadow. He sees her shadow cast on the curtain, not on the floor where it should be according to the position of the setting sun from the window bay behind her, cross-town to the West Side. He sees her shadow, as he has seen it many times before, cast unnaturally. Although he has expected it, he turns away his head at the sight.
What Spark cannily does not point out is that every time this anomaly is pointed out, Elsa's shadow is pointing toward the East River. It is not the river that is important, but the East: Elsa's shadow points toward Europe, where she and her husband Paul once worked for a secret World War II program broadcasting British propaganda using German war defectors. Elsa suspects that one of these defectors, perhaps planning to kill them, has appeared in New York, posing as a shoe salesman.
This is the nature of Elsa's madness: she is stuck in time. Even in New York, her life revolves around her time in this secret program, it points backward--not only does her shadow symbolically reach toward it, but its backwardness suggests the reversal of the earth's path around the sun, and the reversal of time itself. Nothing is as real or relevant as this period of her life:
[Paul says,] "You did call me yesterday, you know. Don't you remember?"
"What has yesterday got to do with me?" she asks.
Time in Hothouse is the mirror-image of time in The Girls of Slender Means, where each individual moment is viewed as a single point in a long expanse: here, the expanse rests on a single point.
The themes are the same, then, but the approach is different: Hothouse is much more experimental, from the use of present tense to the loose absurdism, in which Spark isn't quite comfortable. I liked some of it, especially this moment, about one of Elsa's friends who breeds silkworms, keeping them in her bra for warmth:
Garven screams. His eyes are on the Princess's bosom. He screams. Under the protective folds of her breasts the Princess, this very morning, has concealed for warmth and fear of the frost a precious new consignment of mulberry leaves bearing numerous eggs of silkworms. They have hatched in the heat. The worms themselves now celebrate life by wriggling upon Princess Xavier's breast and causing Garven to scream.
But ultimately Hothouse is underserved by Spark's style, which is too brisk and controlled to really allow absurdism to flourish. The twist, too, is deeply unsatisfying--and perhaps you may figure it out yourself if you think on the image of worms, celebrating life.
What is more interesting to me is the relation of Hothouse to Spark herself, who once worked in a program like Elsa's, and who suffered from a form of madness brought on by diet pills. Spark thought that T. S. Eliot was embedding messages to her in his works and in newspapers; in Hothouse Elsa's husband Paul believes the German defector/shoe salesman is scrawling messages for them on the bottom of shoes. Are we permitted to draw the line, and wonder if Spark's own mental illness is connected to her time in the propaganda program, which made a business of messages and codes? Did Spark herself feel anchored to her wartime experiences? It does Hothouse no credit that these questions point toward a story far more interesting than the one she published.