When a vengeful alien threatens to destroy Earth, a reluctant young drifter must live up to his father’s reputation as a Starfleet Captain and stop the invasion.

It has clear objective and an evident inner motivation (the successful, glorious father, etc.). I like it and I think it works.

Perhaps a little more specific info on the alien? Is it an "alien spaceship" or a whole "alien fleet?" Perhaps the drifter has to organise the Earth's fleet, to deal with an invasion of a larger scale.