My favorite volume of the series remans The Light and the Dark (1947). The storyline is simple; the novel focuses on Roy Calvert, an able young researcher into ancient languages trying to translate an extraordinary document, what is believed to be the only surviving written work of the Manichees, hitherto known only by the writings of their enemies, such as St. Augustine. In truth, a handful of fragments and isolated quotations exist as well, but the manuscript Calvert is working on, a psalm-book, provides the best chance of understanding the Manichaean world view as communicated amongst adherents to that faith, with its distinction of the world into--you guessed it--Light and Dark.
The Psalm-book is real enough; it was translated by Charles Allberry, affirmed by Snow's brother Philip to have been the model for Roy Calvert. Like the fictional Calvert, Philip Snow asserts, Allberry suffered from terrible bouts of depression, and moments of manic elation, but was also charismatic, charming and kind, especially to those who were poor, oppressed, or unhappy.
Snow makes Calvert very real, and sympathetic; it doesn't hurt that the character is that rarity, a fictional wit whose dialogue is in fact witty. For much of the book, he tilts quixotically against those in power who have become pompous, and use learning for fame, or to keep others down. His characteristic method is to solemnly interrogate them, tripping them up in logical inconsistencies, or revealing their hypocrisies in deadpan dialectic.
These amusing interludes, as well as some society life, are punctuated by Roy's struggle against his own "oddly mechanical" affliction--depression, destructive elation, relief, alternating in phases only the length of which are unpredictable--leads him to try to lose himself--in God, in women and drink, even flirting with Fascism (the novel is set in the mid-Thirties into World War II).
This last is an interesting, and risky move. It happens quite late in the book, after we have come to like Calvert very much indeed, and is a shock. It's profoundly narratively counterintuitive to have the character drawn to fascism be sympathetic (in Powell's Dance, it's Widmerpool who is a quite unlovely, though interesting figure). Calvert's attraction to fascism causes for the first time a strain in his long friendship with narrator Lewis Eliot, law don and generally reasonable man, himself a firm anti-Fascist, as was Snow, from the get-go. Calvert, no political thinker, is drawn to it as a means of throwing himself away in hopes of escape from the crippling, debilitating depression he suffers--he is a specific instance of Erich Fromm's "Escape From Freedom." Even while he finds himself drawn to it, Calvert is revolted by its bigotry and antisemitism, as well as its disdain for the odd characters Calvert loves--he even risks his life to save a Jewish couple from the Nazi regime. It's a brilliant portrayal of cognitive dissonance.
Ultimately, Roy himself rejects the Reich as "a feeble simulacrum for his search for God", admitting to Eliot that "I was clutching at anything of course," and sadly describing it as "my last grab." (Ch. 33)
So Roy gives in, and tries to live with his affliction, while he serves in the War. First in intelligence, but then, as the depression closes in on him, he chooses to join the RAF, after enquiring of Eliot what is the most dangerous duty to be had. He becomes a bomber pilot, because he wants to die but can't quite kill himself. In his surrender, he marries, and his wife bears a daughter. And Roy becomes, ironically, free of the cycle that has driven him to choose death over life; he finds, at last a certain peace. Now that he no longer wants to die, though, he is stuck; "One can't change one's mind," Roy admits, "It[war] holds one to it." (Ch. 38)
He dies of course. We get one last flash of his diabalerie, though. Spending a day with Eliot in the London Library between flights, he has a shock:
"Lewis," he said, in a clear, audible tone, "I'm losing my grip. I've forgotten the Soghdian for fish." He looked up, and saw a member, fat, stately, in a black hat and fur-lined overcoat, walking out with books under his arm. "I wonder if he knows," said Roy. "I need to ask him."(Ch. 38)
Roy stepped lightly in front of the fat man and gave him a smart salute.
"Excuse men sir," he said, "but I have forgotten the Soghdian for fish. Can you help me?"
"I'm afraid not."
"One ought to keep one's languages up," said Roy: his gaze was solemn, reproving, understanding. "It's terrible how one forgets them Isn't it?"
Hypnotized, the member agreed that it was. Roy let him go.
On the bus to [Eliot's flat], the word returned to Roy. He professed extreme relief.