This should not be confused with the M. Night Shyamalan movie by the same name. It should also not be confused with an actual "Happening", which in the 1960s was a weird art experience thing where people would show up at a place and hang out with no real plan. It was sort of like flash mobs are now, I think. When you hear Austin Powers (or the character in Beyond the Valley of the Dolls from whom Mike Myers borrowed the line) say "It's my happening, baby, and it freaks me out!" that's what they're talking about. A Happening.
But there is no Happening in The Happening. It starts with a big drug orgy, then four listless characters escape from the police and accidentally kidnap a mob boss. Actually, he kind of kidnaps himself. He's a take-charge kind of guy. Then no one pays the ransom, so he raises it. Which is not the way it's supposed to work. Normally the hostage just sits there tied to a chair or something. Anyway, it ends on kind of a nihilistic, existential note, the way movies in the sixties often did. You should see Dirty Mary Crazy Larry, for example.
The novelization does its best to make the random events interesting. But there's only so much you can do with characters like this. Practically as soon as the four protagonists have met, on page 13, this happens:
Full sunlight had turned Sandy cynical.
"He's a cheap hustler who wants to be legit," she said.
Without taking his right hand from the wheel, Taurus swung his left in a half circle and backhanded Sandy hard and full in the face.
Classy, eh? And Taurus is one of the heroes of this little epic. So's Sandy, who a few pages later has the most memorable line in the book (or, I suspect, the movie):
"Hit me again," she suggested. "A real wham. Maybe I'd feel something anyway, hey Taurus?"
Yeesh. People in low-budget movies in the sixties were serious weirdoes if you ask me. Anyway, Sandy's the only real reason anyone remembers this movie even exists, because here's a picture from the back cover:
That's Faye Dunaway in her first starring role. Later that year, she'd also appear in Bonnie and Clyde, which is a much better movie about directionless clowns committing crimes.