The conversation with Kade and indentifying Gisette are two different things. The second takes you to figure it out based on clues and mystery hunting. The conversation with Kade is about the death of the servant. Hope that helps <3
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The Kade scene for mystery hunting requires:
first passing a 60 courage or 80 manipulation check ---- > correctly answering his questions --- knowing the correct reason the servant was killed (requires figuring out a certain persons plot against you) ----- > correctly guessing Kade's motivation ----- >correctly guessing the method of murder / and three other correct theories of what might have happened (wrong guesses will work against your total score here) --- then passing an interpersonal insight or persuasion check
if you have done all those then you unlock his confession scene
hope that helps <3