So 'Oh' the little alien pimps up Tip's car (Tip being the only surviving human outside of a concentration camp type colony), and together they go to find her mom - with a detour first to save the day and delete his e-invite to the rest of the galaxy - including the enemy Gorg.
So they get to Paris, and locate Boov Central Command where a disguised Boov can cancel his e-invite. The other Boovs are still on their case - and they were too late, the Gorg have come to earth. They both head off now to Australia, to find Tip's mom, but are attacked by a Gorg drone. They manage to destroy the drone, and use some Gorg technology to get their car all the way to the human colony.
But the Boovs are in distress, and have decided to run away again. Oh catches the last shuttle away from Earth, leaving his friends to a nasty fate.
He has a change of heart, and convinces his fellow aliens that they shouldn't run but should hug and protect each other. Captain Smek disagrees, but the others are on Oh's side and pass him the Shusher of power. Oh turns the ship around.
First,he helps a despondent Tip find her mom - then has an idea. Bravely, he walks up to the imposing Gorg ship - and hands the Shusher rock back to the enemy Gorg commander. He opens his mask, MIB style, and inside is an innocent enough looking starfish - who opens the rock and we can see all his tiny babies. He apologies for being grouchy.
As it ends, all humans seem to have forgiven the aliens, and they hold a big party at Oh's place -- but the invite has still reached a large part of the galaxy and many aliens are on their way to Earth.