This race tried to make Earth their new home
The Zygons homeworld is unknown but it was destroyed. They have little suckers around their bodies and they are quite tall. They have avrious types of technology including Duplicates and Cyborgs. Their Spaceship crashed to Earth and their leader Broton instructed them to duplicate the towns people. Their ship crashed at the bottom of Loch Ness and they had a monster called the Skarasen which was half animal half machine. They waited for a rescue ship which could take centuries to reach Earth. When it got close Broton lead to the Zygon invasion of Earth. Broton stole the Duke of Forgill and used his body as a disguise. They had a tunnel from their spaceship leading to the Duke of Forgill's Castle.
UNIT went to Scotland to investigate what the Zygons had planned. The Skarasen was known as the legendary Loch Ness Monster. The Zygons used nerve gas to put eveybody to sleep so that the Skarasen could walk over them. The place was called Tullock. Broton thought that he could infiltrate the International Energy Commission Conference down in London which was quite a distance. They almost activated the Skarasen to kill the head of each country. Broton's plan was foiled when his Zygon Warriors were dead and when the Brigadier Lethbridge-Stewart shot him and saved Earth once again from another attack.
They appeared in:
Season 13: Terror of the Zygons