In Sweet Tooth Episode 7, Gus dad works in a company as a cleaner while Birdie was the scientist in the same company. One day they met in the bar, and One thing leads to another, and they spend time together till 2 am. Birdie got a call that the government is seizing her research, so she and Gus dad went to the company to save the research. Gus dad found that the research was the Gus. Gus is the name of the research on which birdie was working. They took Gus, and Gus dad went away to the mountain to protect Gus while Birdie went back to destroy her research.
Gus team finally get to their destination, but there was not her mother but a friend of her mother. She said that the Birdie went away to search the Gus and never came back. She also gave Gus a key and told him that her mother wants her to give it to him. Gus and his team went to the room where they all find out about the research. After knowing that they both are not his birth parents, he was hurt and he runaways in the forest and keeps on running until getting exhausted.