Things get personal between Castle and Beckett on Monday night.

In the following clip, the former confronts the latter over getting in too deep while investigating her mother's murder. After all, Castle reminds his partner, everyone associated with that case in dead.

But the conversation turns from there, as the question of just what, exactly, these two are to one another comes out. How will this all lead to the demise of a character? We'll have to tune in and find out...

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.