When a young woman returns to her family for the burial of her brother, her doubtful past will envenom the reunion and reveal her true intentions.

1. 1. Give the character a better adjective. Young is value neutral and doesn't tell us much about the character. If she's going to be revealed as some sort of sinister or vengeful person, then using adjectives like naive or idealistic would set up the twist better. Also use an appropriate adjective to characterize the family, so we understand what the relationship between the woman and the family is. Like, is the family evil or manipulative, or is it emotionally distant, etc.

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1. 1. The logline is too mysterious. You should tell us what the girl's doubtful past and her true intentions are so we know what the exact goal and conflict for the man character is.

      Your logline reminds me of Festen. There, the logline would be:

      A young man attending his father's 60th birthday along with the rest of his family reveals that he was sexually assaulted by the father for years. Now he must get the father to acknowledge his crime in front of the extended family who have congregated for the celebration.

      Maybe this could be a model for your logline. Character reveal at the end of the first act, and then set up a concrete goal for her.?