A desolate fugitive is forced out of hiding when his vengeful ex-partner in crime kidnaps his son.
‘Desolate’, as an adjective applied to a person means they are ‘wretched or greatly unhappy’. Why is the hero so unhappy before his son is kidnapped? Considering he is in hiding, did you mean ‘reclusive’?
In general, the story you describe is too generic. I feel like I’ve seen this movie a million times in one form or another.
Try and spice it up by suggesting a greater struggle for the hero, e.g. he’s a successful fugitive living in Mexico and must cross back across the border and risk being caught by the FBI in order to rescue his son from his vengeful ex-partner in crime.