A police officer kills a powerful alien, and many Earthlings are infested by another. The second alien leader and the officer’s future-timeline son hold grudges against the cop for murdering their dear ones.

UPDATE #2:

The opportunity to prevent his father from murdering his mother urges a young fighter to travel through time with his friends, to when a war was raging between humans and a deranged alien.

?

>>>Ulterior motivation

Which is?? The prime motivating event, conviction, or value should be disclosed, not hidden.

>>>Ulterior motivation

Which is?? The prime motivating event, conviction, or value should be disclosed, not hidden.

UPDATE #1:

Ulterior motivation urges a young fighter to travel back in time with his friends, to help end the war that once raged between humans and a deranged alien.

The inciting incident leads to the lead character having a goal.

You set the story up as if the police officer is the lead character and killing the alien is the inciting incident.

But I have no idea what the lead character's goal is.

Agreed with what Robb Ross said.

Some things in this logline are not very clear. What is the inciting incident? Clearly the police officer killing the alien isn't. Also when you say many earthlings are infested by another? Do you mean that they are infested by the same alien? It controls multiple people?

Also "holding a grudge" against the cop for killing their loved ones isn't a cinematic goal that our lead (the cops son?) will strive for. What does your protagonist do for the 2nd and 3rd act of the film? Or is this a series?