After a small recap of part 1,Martin Diana and Java realize Billy was on the ship.So they call MOM.When they tell her the invaders were calling Billy Ganthar,she calls them back.So when they go back she tells them about Billy's secret past.Billy used to go by the name Ganthar and was the leader of the invaders.Ganthar was the most savage and powerful alien.He used to destroy planets by stealing their resources leaving the planet lifeless,then they moved on to the next.Ganthar then got tired of it and snuck away.He crash-landed on Earth in 1947,causing the Roswell Incident as well as Area 51.He joined the Center and created a new form and a new name.The remaining alien contacts MOM and offers to trade Billy for his two partners and MOM agrees and assigns Martin, Diana and Java to make the trade. Martin doesn't trust the alien and wants to organize a commando raid to free Billy but MOM thinks it's too risky. Martin swipes a vial of freezing fluid off MOM's desk since they discovered in part 1 the aliens are allergic to cold.So they go to New Mexico where the alien is with Billy.Billy warns Martin not to do the trade because if all three of them were together,they would be able to operate the transmission beacon.The alien hits Billy with this stuff.This makes Martin throw the vial,but the alien creates a force field and the vial freezes Martin,Diana and Java.The invader frees the other 2 aliens and they take off with Billy.In the ship they threaten to exterminate Billy since he does not not want to rejoin them but in the mean time he can watch Earth be destroyed.Then they call the mothership using the radiation they stole in part 1.MOM calls and wants them to come back.Martin calls Billy and gives the coordinates for the ship.They ignore the call MOM gave to go back.They go through the pyramid and think they found Billy.But it was really the three aliens in Billy's form so they end are locked up with Billy.He tells them that the aliens are closer and they won't need the beacon.Billy changes back into Ganthar even though he doesn't want to.Then he breaks free.He then destroys the invaders and the transmission beacon.However Ganthar loses control and tries to attack Diana.Then Martin sees it is too late and the mothership has arrived and is destroying everything.So Ganthar goes into a ship and he destroys the ship and saves the world.However,Ganthar was hit as well and there was no sign that he was still alive.So back at the Center,everyone sadly remembers Billy.Then Billy comes in suddenly and he is still alive.He says he is glad the eject button worked.MOM wants to give him a chip that will prevent him from ever changing back.Billy doesn't accept it and says he will never change back.Diana says they could give it to Martin to keep him from from being a goof but then takes it back and says it wouldn't be that strong.Everyone laughs,except Martin. ..Read the full recap
If Billy was the alien in the Roswell Incident,he must be over 60 years old.It also must mean he has been working at Center for 60 years.
This episode is mostly about Billy.