Yep, the title pretty much sums it up. Siblings Elizabeth and Paul are complete terrors... self-absorbed, bratty, pretentious, greedy, selfish terrors. They mooch off of assorted benefactors, shirk all responsibility, flirt incessantly with incest, and devise manipulative schemes to fuck with their friends and enemies. (And it's often difficult to say who of the characters fall into which category.) Naturally, even though they are only 15 and 17, all this goes on in an artificial bubble which is completely devoid of any adult supervision. It's the old teen fantasy behind "Cruel Intentions" and "Beverly Hills 90210".
The fun and games chug along with absolutely no adverse consequences for anything they do, until the last 10 pages. A blurb on the back of the jacket compares this story to a Greek tragedy. The difference is, at the end of a Greek tragedy, you aren't glad that everybody is dead.
*Bonus antipathy points for Cocteau's shitty, overly self-conscious, "arty" minimalist illustrations.