Constructing an original, entertaining and intelligent plot is hard work, but that should not mean you should settle for the easy option when writing a screenplay. In fact, the opposite should apply. If it’s difficult to come up with something original then push yourself as a screenwriter that much harder. Force yourself to be innovative because if you do you will undoubtedly produce something much more engaging and satisfying for an audience in the process.
Many writers of fiction, especially crime fiction, use a MacGuffin in complicated plots to drive a story forward, and Alfred Hitchcock (who coined the term) was one of them. The whole point of the MacGuffin is that it is irrelevant. As Hitchcock himself explained, the MacGuffin is: “the device, the gimmick, if you will, or the papers the spies are after… The only thing that really matters is that in the picture the plans, documents or secrets must seem to be of vital importance to the characters. To me, the narrator, they’re of no importance whatsoever.”
In the golden era of Hollywood, writers and directors were never always as concerned as their modern day counterparts to get all the facts straight. So long as the women looked sexy, the men looked rugged and there were guns and chases the Hollywood Execs were happy. To illustrate the point, you may have heard about the classic Howard Hawkes movie The Big Sleep with Bogart and Bacall, based on the novel by Raymond Chandler.
In the story there was confusion surrounding the death of the Sternwood family chauffeur, a character named Owen Taylor. Apparently somebody sent a telegram to Raymond Chandler asking him “Who killed the chauffeur?”. He replied “Damned if I know.” It’s an amusing anecdote but I know that from my experience when developing a screenplay with producers and development executives that you must have an answer for everything and that nobody would be impressed with a reply like that.
So to avoid such professional faux pas and to make sure the logic of your crime thriller is coherent I suggest you do your utmost as a writer to iron out all the creases in your plot BEFORE you present it to anyone. And most importantly, do not rely on coincidence to be the solution. If you hero just happens to find a gun under the bed during a frantic struggle with his nemesis then that’s poor penmanship. If your heroine loses her job and then just happens to bump into someone who offers her another, that’s lazy.
As always, there are exceptions to the rule and sometimes a particular story or genre can get away with it so long as it’s an intentional screenwriting choice and clear to the audience as such. But generally you should set up events so they do not seem coincidental. If it strikes you as obvious then try to figure out another way around revealing a crucial piece of information or engineering a chance meeting without it being too contrived. If that fails, you could always try to conceal your coincidence behind a powerful moment of action or drama and hope the audience don’t notice!