The Three Act Structure

Syd Field proposed a theory called the Three-Act Structure, which he claimed most screenplays followed. It also applies to Thriller Films and works like this:

As you can see, the tension builds up throughout the film. During crises, something tense will happen but will quickly be resolved and so the tension decreases once again. This happens a few times throughout the film before you hit the climax. This is something that is very tense and is the pinnacle point of the film. Once the climax has been resolved, the tension drops completely until you hit the equilibrium once again. During the tension decrease near the end of the film, this is known as the denouement.
The Three-Act Structure may also apply to Thriller films. The tension will continue to increase throughout the film as more and more information is revealed to the audience, and then you get to the end of the film when all is made clear to the audience and you go back to equilibrium.
Despite the fact we are only making a Thriller opening and so won't need to worry about the structure of the entire film, it is important to remember that during our opening it wouldn't be too tense. The only thing that may happen during our opening is the first crisis.