About Adaptations

Other than a post I came across about someone wanting to adapt Frozen into an Episode story, I haven’t really seen this discussed here.
How does Episode handle stories that are inspired by existing TV shows or movies? For example, if someone wrote an Episode story without using the original title, character names, or branding, but the overall plot and story were still quite similar, would that still be considered copyright infringement?
At what point does a story stop being an adaptation and become an original work that’s simply inspired by the source material? Is there a general rule of thumb for how much needs to change?