Certainly one of the more challenging aspects of writing a thriller is developing the investigative plot thread typically part of them--figuring out how the secret agent who has to crack a conspiracy with the clock ticking actually makes their way to that point. The writer is obliged to make it compact and dramatic and conclusive, while centering it on the figure of a single protagonist (if only nominally), and at the same time make it all logical and realistic. And at the same time, avoid being predictable or repetitive.
This, of course, is a tall order, and writers rarely fulfill it. That is not at all surprising, given the ways in which all these imperatives clash--the plausible and the dramatic, for instance. Naturally writers tend to work around the problem, presenting rather less investigation, less ratiocination, less putting together of the pieces than appears the case at first glance. Putting it another way, they rely on sleight-of-hand to make a simple, implausible and sometimes incoherent sequence of events look like a winding, compelling intrigue.1
Even if we do not ordinarily think of them this way, the truth is that we all know the devices well. The writers put crucial clues right in front of their protagonists, courtesy of incredible coincidences--having them walk right into a plot, or catch a crucial bit of conversation when they eavesdrop, perhaps--and give them the benefit of convenient villains, who are far too given to foolish gestures, elaborate games and arrogant speeches for their own good. (The James Bond series epitomizes the tendency, particularly in classics like Goldfinger and Thunderball.) The authors spare their protagonists much of the trouble of putting the picture together by having someone else do the hard and usually undescribed work of unraveling most of the mystery, drop it in their laps and then exit the stage so that the latecomer gets to be the big hero. (John Buchan did this for Richard Hannay in The Thirty-Nine Steps.) They endow their heroes with unlikely bases of knowledge and intuitive faculties that let them connect very small, very widely dispersed dots in ways that reason simply cannot, and an incredible self-assurance that props up pronouncements that simply do not hold up to any serious scrutiny. (Two words: Sherlock Holmes.) And sometimes they do not even make that much effort, not bothering to have their heroes connect the dots at all. (The story goes that in the midst of filming the movie director Howard Hawks, uncertain as to who killed the chauffeur in The Big Sleep, telegrammed Raymond Chandler asking who did it--and that Chandler replied that he had no idea.)
While actually immersed in a thriller, however, we tend to overlook all this. After all, the investigation itself is usually buried in a narrative of danger and romance and travelogue and all the rest of the things that make up the reading experience. (Indeed, the mystery is often just an excuse to connect up scenes of whatever the author happens to find cool--action scenes, witty banter, philosophical interludes and so forth.) We are supposed to be left guessing at everything that's happening, so we usually defer our judgment until later. (The whole point is to keep us in suspense, after all.) And then after everything seems to have been made clear, we tend to take the concluding explanations at face value, because if we had a good time getting there we're likely to be generous, and because going back and checking is more work than we usually bargain for in a mere "entertainment."1
And because if we were really picky about such things, demanding the same level of plausibility and rationality in our fiction that we do other things in life, we probably wouldn't read thrillers, or any other sort of fiction for that matter--the phrase "willing suspension of disbelief" existing for good reason.
1. How rarely we actually do this is demonstrated by the sorts of summaries we are likely to find of much of this genre when we go looking in books, or on the Internet. Even when the author has no compunctions about writing in spoilers, they rarely reconstruct for the reader the way in which one thing led to another.
A History of the Spy Story, Part II: The Life of a Genre
A History of the Spy Story, Part I: The Birth of a Genre
The Triumph of the Thriller: How Cops, Crooks, and Cannibals Captured Popular Culture, by Patrick Anderson