When Noah Webster wrote the dictionary in 1757, he created the English language, but more importantly he created the word super. Well, when our neighbors across the pond found out about this new language a hundred years later, they decided to make a dictionary of their own, but they weren't satisfied with the word super. The OED needed a better word, so James Murray and some looney named Minor added a letter to it, thus inventing the word superb. That is what this book is.
Oedipa Maas is our protagonist. On page 1 she is summoned to execute the estate of a billionaire friend and heads off to southern California to do so. Once there she discovers a clandestine postal system with roots in the middle ages that's been illegally competing against the USPS in a massively orchestrated conspiracy. The muted post horn is their symbol and it's seemingly graffitied everywhere once she starts to look for it.
The book is filled with references. Everything is a reference. I don't even think Pynchon would catch them all if he reread it. He pokes fun at cultural phenomena like Beetlemania and urban sprawl (read California). He mocks used car salesmen, psychiatrists, commercial radio, stamp collectors, pseudo scientists, sex, marriage, and drugs. There are words in Spanish, French, Greek and Dutch. The novel is short in length but huge in scope. Yes it's about a conspiracy, but you won't find it mixed in with those cheap paperback mysteries you find in the grocery. It's not just plot. It's dense.
I think it merits a second read. I'll probably go back through it next year. This is the first book by Pynchon I've read, and I've heard his others are much longer, so it's a good starting point. Read it and enjoy it.