When a man sets out to destroy the family that destroyed his, he ends up falling for the ingenue daughter.
First of all, what do you mean destroy a family? Make the parents divorce? Make them go bankrupt? What is it that they have done to him that he can do back to them?
So he falls in love with the daughter. Then what? This sounds like the big event. Then, there has to be an action. Must he reverse the revenge plan? Must he detonate the bomb?
It sounds more like a comedy to me. Running against the clock to undo what he has set up. Perhaps it ends with forgiving them and marrying the daughter.
When a vengeful man falls for the daughter of the family responsible for his financial demise, he must [ACTION].
When a bitter man falls for the daughter of the family he plans to avenge, he must [ACTION].
Never start a logline with When. Start with the protagonist, then provide the antagonist, conflict, & stakes. Avoid commas. 25-30 words max, the shorter the better. No vague notions — be specific about who the characters are and what they want/need to do.
Try not to repeat words, such as “destroy.” Not only is it already unclear what this means or what it involves, but the redundant use makes the entire storyline more vague. Also unclear: saying he falls for “the” daughter…of the other family? Why? How? Why is this a problem? What was the problem in the first place?
A logline shouldn’t force questions just to comprehend the story. It should make people interested in reading more.