Faced with a massive financial battle, a down-on-his-luck man has to urgently pay for his son’s emergency operation. It is not until he stumbles upon his long lost friend and he returns a long forgotten favor that his tilted world suddenly becomes upright again and his life changes for the better.

One thing I noticed. You have the situation: His son needs an emergency operation; which sets a course of action: He must acquire the money, But what is standing in the way? Because in your logline suddenly a long lost friend appears and solves his problem.

?When his son suddenly needs an emergency operation, a cash strapped (Give us an occupation) devises a plan to cash in an old?favor from a rich former friend.?

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As per dpg, also check out the log for Breaking Bad for ideas...

A high school chemistry teacher diagnosed with inoperable lung cancer turns to manufacturing and selling methamphetamine in order to secure his family's future.