(Disclaimer: English is my second language, so I want to apologize in advance for there may be mistakes in the text below. If you find any, please let me know so that I can correct it. I'd really appreciate it. Thanks.)
It's been some time since I last quit reading a book before finishing it, but with The Fold, by Peter Clines, I was tempted to do so almost since the very beginning. In fact, although I technically read it until the last page, I only skimmed the last third of the novel. I've read some very positive reviews (that's what made me give it a try) and your mileage may vary, but I found this novel to be very weak in almost every regard.
The Fold is, for its better part, a SF mystery (later, it turns into something else, but it'd be kind of spoilerish to tell into what), a subgenre that I'm not very fond of but that I can enjoy now and then (for instance, I did like Superposition quite a lot earlier this year). In fact, the plot of the novel, although very conventional, is not especially bad. The mystery is (sometimes) intriguing and the twist is at least coherent with some of the earlier revelations.
The main problem with The Fold, then, is not its plot, but its writing. The dialog is supposed to be smart and witty, but falls short all the time. The jokes are lame (if you are not rolling your eyes the first time someone replies "Not now" to "Fuck me" I think by the tenth you will be) as in, for instance, something like:
"What else do you name a chimpanzee that changes the world?"
The characterization is not much better. The main protagonist is completely unbelievable, with his photographic memory and his out-of-the-chart intelligence. He is supposed to be kind of a modern Sherlock Holmes (although he works as an English High School teacher), but with the exception of a couple of tricks that the author adds just to make his case, his deductive powers do not seem to accomplish much. The secondary characters, in turn, are clichéd and one-dimensional (which is kind of ironic in a novel about interdimensional doors), including the obsessed scientist and the girl that falls for the protagonist just because.
The novel is also full of small inconsistencies, little details that are mostly not that important to the plot, but that constantly annoyed me. What is more, the depiction of the work of the scientists is so inaccurate (especially in the case of the computer programmer) that it would be funny if it were not an important part of the plot.
All in all, I can only recommend skipping The Fold. The writing is poor, the plot is unoriginal and implausible and the characters lack any depth. I was tempted to suggest that it might be passable as a beach read, but I did actually try reading part of the book at the beach and it didn't get any better. If you feel like reading a good SF mystery, I'll give Superposition, by David Walton, a try instead.