I am an only child (TN)

My father is married to a very vindictive and evil woman. I am an only child and she has 3 from previous relationships, none between them. He has told me that he hasn't made a will so that in case he passes before her I'm to go retrieve money he's hidden and left for me specifically to take her to court for half of the estate. I'm completely ignorant to how this stuff works. Can anyone explain where I'll stand in such a situation?