The photos David finds are all taken from the previous episode "Beachhead". The alien ship is from the opening title sequence, and the shots of the regeneration cylinders are from the power station.
Opening Narration: Is it an intrigue or paranoia? There was no doubt in the mind of David Vincent, a renowned physicist, Doctor Curtis Lindstrom discovered the truth, the invaders were on Earth and in a week, in a meeting with his colleagues, Doctor Lindstrom would give the news to the world and then, perhaps David Vincent could relieve his charge, everything seemed so simple.
Closing Narration: For David Vincent another beachhead was destroyed. For the invaders, it was proved that the human race could never be enslaved.