Crafting your own engaging story out of someone else's creation or a historical event is daunting, but Oscar-nominated screenwriter Robin Swicord has had plenty of experience with it, having penned successful adaptations of Memoirs of a Geisha, The Curious Case of Benjamin Button (originally a short story), and even classics like Little Women. In her Master Class on Adapting a Screenplay From Source Material, she reassures screenwriters that “It is important to remember that you have the right to approach material any way that you see fit. People worry about which is better, the original or adaptation; Don't think about that. Put it out of your mind. You have a right as a reader to go to material, to face it.”
At some point before you can fully make the story your own, you have to get rights to it. In the case of a book or short story, Swicord suggests approaching an author personally. She adds, “Sometimes, the approach is best done with a screenplay in hand. What you lose in that case is that you spend a lot of time writing a spec screenplay that you don't hold the rights to.” She warns, “It's not wise to just assume that if you love to book, you can just take it and write something, because a book very easily can come under option by someone else, and so your work will be for nothing.”
To avoid that scenario, Swicord says it might be better to write a “very impassioned email or letter to the author through their publisher. Try to contact them directly and have a literary discussion so that they understand what your intention is,” and attempt to convince them to let you have a shot at adapting their material.