Inverted Depth Mask?

I'm very new to working with shaders, so I have very little understanding of how this would work. I need a shader that would be applied to an invisible plane which renders only objects that are behind it. Preferably, but not absolutely necessary, objects in front of the plane wouldn't be rendered either. So only objects that are directly behind the plane get rendered.

For example:

In the scene below, adding the plane would only render the area it occupies.