Some loglines are so great that they instantly conjure numerous circumstances one could expect from the movies they go with. Take the logline for Les Diaboliques (1955) from IMDB, for example:
The wife of a cruel headmaster and his mistress conspire to kill him, but after the murder is committed, his body disappears, and strange events begin to plague the two women.
I even love how they single out ‘his body disappears’ with commas to emphasise the creepiness therein. It’s great, no? It makes you wonder so many things: Did they kill him? Did someone else see and is taking revenge? Why are the two women friends? Or are they enemies with mutual interests? What interests? How did they meet? What are the ‘strange events’? And so on. The logline sells the movie so well and also gives the writer’s imagination unbound freedom in this regard. It sets us up for a doozy.
It’s rare to develop a springboard like this that allows for multi-directional storytelling. In essence, you could tell the story over and over again and change it each time, just enough, to get something completely different. It’s what would get you a good sale if you were just pitching the idea. Indeed, a remake was made called Diabolique with Sharon Stone in 1996. Hollywood understood the idea was solid and that they could easily get a writer to rewrite with the initial premise intact.