Picnic at Hanging Rock by Joan Lindsay

She felt herself choking and tore at her frilled lace collar.  'Miranda!'  The strangled cry came out as a whisper.  To her horror all three girls were fast moving out of sight behind the monolith.  'Miranda!  Come back!'  She took a few unsteady steps toward the rise and saw the last of a white sleeve parting the bushes ahead.

'Miranda... !'  There was no answering voice.  The awful silence closed in and Edith began, quite loudly now, to scream.  If her terrified cries had been heard by anyone but a wallaby squatting in a clump of bracken a few feet away, the picnic at Hanging Rock might yet have been just another picnic on a summer's day.  Nobody did hear them.  The wallaby sprang up in alarm and bounced away, as Edith turned back, plunged blindly into the scrub and ran, stumbling and screaming, towards the plain.

The girls at Appleyard College in the state of Victoria, Australia, go on a Valentine's Day picnic to a famous geological formation called Hanging Rock.  Among them are Irma, a noted beauty, Miranda, very popular, and Marion, the brainy one.  The three of these, followed by a homely and unpopular girl named Edith, set off for one last look at the rock and never come back.  Edith returns in hysterics, but can provide no information about what happened; a math teacher, Miss McCraw, is pronounced missing also.

There's something recognizable about this setup: it sounds like any number of prestigious police procedurals that begin with a murder or a missing girl, or a whole troop of missing girls, like this one.  (Unsurprisingly, Amazon recently made a series out of Picnic at Hanging Rock, which was also made into a cult movie in the 1970's.)  But those series are inevitably backward-looking: they are interested in uncovering a past that has been hidden behind quaint towns and admired families.  Picnic at Hanging Rock, by contrast, is interested in the progressive effects of the girls' disappearance: a young man named Mike, enamored by a single backwards glance from the otherwise unknown Miranda, begins to obsess over finding the girls; the headmistress Miss Appleyard begins to fret about the financial health of the college as girls' guardians have them withdrawn; conflicts between teachers and students are intensified and laid open.  Lindsay describes the process a drop in water that radiates outward, irrevocably changing everything in its wake:

The reader taking a bird's eye view of events since the picnic will have noted how various individuals on its outer circumference have somehow become involved in a spreading pattern: Mrs Valange, Reg Lumley, Monsieur Louis Montpelier, Minnie and Tom--all of whose lives have already been disrupted, sometimes violently.  So too have the lives of innumerable lesser fry--spiders, mice, beetles--whose scuttlings, burrowings and terrified retreats are comparable, if on a smaller scale.

Ultimately, Lindsay decided not even to include the chapter she wrote describing what happened to the girls.  (Although, judging from the description I've read of it, it's so bizarre and fantastical it doesn't seem like it would have explained much!)

The picnic described occurs in 1900, and though Lindsay wrote it in the 60's, the novel often feels like it's contemporaneous to its events.  It has a kind of Victorian stuffiness, and a willingness to lead the reader along imperiously ("The reader taking a bird's eye view...") that went out of fashion with modernism.  Because of that, its weirdness often catches you off guard: Mike's dreams and visions of a white swan taking off, for example, or the Grand Guignol final scene in which Miss Appleyard brings the whole thing to a kind of eerie, circular conclusion.  And as much as Lindsay insists that the novel's plot has a kind of inevitability to it that the girls' disappearance sets into motion, what happens often seems only tenuously connected to it.  Is it enough to say that if something might not have happened without the disappearance, that thing happened because of it?  There's something strange about the novel's conception of causation that gets hidden behind the antique style.

I was intensely interested in The Picnic at Hanging Rock, although I'm not sure I enjoyed it, exactly.  It's unsettling.  It's unsettling in a way that is hard to describe after you're finished reading it.  It's unsettling because it seems uninterested in committing to its own weirdness, as if weirdness itself is too predictable or ordinary.  Like the disappearance of the girls, it's the kind of book that, when you're done with it, makes you wonder what the hell happened.