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.