Cassie was in charge of a diner after her mother ran off. She lived near Roswell and Area 51 and knew the area well. One day in 1958, while she was serving coffee to her friend Jimmy Stalkingwolf, the Doctor walked in and activated a device from an alien crash landing. Secret agent Mister Dread quarrelled with Jimmy, forcing Cassie to flee with the Doctor and Jimmy. The Doctor, Cassie and Jimmy became prisoners of the military. After discovering the military were working with the Viperox to gain control of the Earth, Cassie and Jimmy helped the Doctor defeat them. Cassie was devastated when the Viperox attacked the local town.
Cassie proved very hospitable, welcoming the Doctor and serving customers.
Even though she can get afraid, Cassie showed amazing courage and chose to help the Doctor even though she knew the dangers. She also showed such compassion, helping the Grey Aliens. She also showed more intelligence than Jimmy, connecting some clues together including how Seruba Velak was the name of the one Rivesh Mantilax searched for.