Lancelot is the only Walker Percy novel that I haven't read in the past couple years, and now that the vague rumblings of an idea for my dissertation have begun popping up in the back of my mind, I'm giving it another chance. It's simultaneously like and not like his other novels--there's a plot in there somewhere, but it's buried in a mental patient's mind, and like Notes from Underground (the novel Percy clearly wants us to think of when we read it), we shift rapidly from trust to skepticism when Lancelot Andrewes Lamar says something.
Language has always been important for Percy. At least half of his nonfiction essays deal with language in some form, building off of Charles Saunders Peirce and forcing linguistics into existentialism. In "The Delta Factor" (from The Message in the Bottle, his first anthology of non-fiction), he goes so far as to claim that language is what makes human beings human beings, and says that it's the key to understanding man in an age where we simultaneously believe we're the image of God and just another animal.
But here the most important things are ones that can't be vocalized. I'm reminded of Kierkegaard's Either/Or, in which our young aesthete, "A," declares the musical to be the erotic and the demonic (and of Melville's Pierre, which has a strikingly similar theme). But here, the unspeakable seems neither musical nor demonic. Lance connects it with innocence--his plan for a new society involves the girl in the room next to him in the insane asylum, who cannot speak but communicates vaguely through taps on the wall. (When Lance attempts to create a code to have an actual conversation, she can't follow it.)
But a new society is necessarily because of an unspeakable evil, the evil that Lance makes it his quest to find. He sets himself up as a knight-errant on an unholy quest, a "quest for evil," a quest to find "one sin, one pure act of malevolence." Doing so would shatter the complacency of the psychiatric age, in which "mothers and fathers who beat and kill their children have psychological problems and are as bad off as the children." Lance finds himself surrounded by "good" people, people whose faults are either not faults at all or at least not their fault, and he's disgusted. Finding one pure, unspeakable sin would destroy the modern world and allow him and Anna to build a new and superior one.
In doing so, he modifies Kierkegaard--the musical-erotic-demonic is a stage (like Kierkegaard's aesthetic sphere) that must be passed through in order to reach something better. I hated Lancelot when I first read it five years ago, but now that I've read the existentialists (and Percy's other novels), it makes perfect sense and has a strange and sinister beauty.