Something along the lines of a psychological thriller.
Very ambiguous opening can have lots of quick cuts and fades.
No actors have to be shown as this creates a sense of mystery and suspense.
Easy to light as a small area is being used. Easier continuity.
Writing notes - close ups.
A whole location doesn't need to be used, just a small dark space that can be lit by lamps...
Possibly use a church - if we can get permission - creates 2 different interlocking scenes.
Inspired by Se7en...