Ep 5. V: The Final Battle: Part 3

Donovan turns himself over to the aliens in order to save his son. Diana hears her colleagues are plotting against her. She tells her leader that only she can succeed because of a spy she has in the Resistance. Willie, a friendly alien, submits to tests so Julie can develop a biological weapon against the Visitors. The weapon, a red dust, is then used against the Visitors with much success