How to make an object visible only when it's located behind a certain plane?

For my game I need to create an object which is not visible for the player unless he looks at it through a special glass which is a transparent plane, once this plane gets between the camera and the invisible object, the proper part of the object becomes visible

I made a badly drawn paint image to illustrate my idea:

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To be more detailed; the glass plane will be static, the invisible objects will move

I experimented with multiple cameras and layers but I can’t come up with anything to achieve this effect

If anybody could help me to come up with an idea how to make something like this I’d be awesome

This is what the stencil buffer is for… Using the Stencil Buffer in Unity Free | Alastair Aitchison

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