Years after his son’s murder, a bitter gangster-vigilante trains a new recruit, but the young undercover commando is there to take the gang boss down?

he's seeking revenge on the gang leader who killed his dad...but the main story is...the vigilante's obsession with protecting the world is tearing his family apart...

I am ignoring the explanation of the story and just going by the logline (as this is the purpose). This logline is way too busy and confusing. For example, because of the word "but" it feels like the new recruit and young undercover commando are different people. Are they? And is the gangster-vigilante the same person as the gang boss? Or not?

Plus, it sounds very much like a The Departed rip off, just on the basis of the logline. What is unique about your script?

against their common enemy...