The first time she appeared on TV was as a guest star on the episode in 2002 of Angel. Director Joss Whedon was impressed and cast her as River Tam on his short-lived TV series Firefly. She also starred in the role for the sequel Serenity. Glau was previously a candidate for the part of a Power Ranger (White Wild Force Ranger Alyssa Enrile) in Power Rangers Wild Force but was unable to beat actress Jessica Rey before meeting Whedon.Glau played the role in the episode "Love Conquers Al" from the TV series Cold Case. The actress had a small role in the film Sleepover, in which she played high school senior Shelly. She was also in the CSI: Crime Scene Investigation episode "What's Gilbert Grissom Doing to Gilbert? " in season two of The Unit as Crystal Burns (the girlfriend of Jeremy Erhart). Glau was the paranoid schizophrenia returnee Tess Doerner in season 2 of The 4400. She became a regular character during season 3 and beyond. Mammoth was also her horror-comedy role. Glau was also featured in ABC Family TV's feature film The Initiation of Sarah. Glau played Cameron Phillips in Terminator: The Sarah Connor Chronicles. This series debuted January 13, 2008. The seventh episode of the series, "The Demon Hand", featured several scenes where Glau, in character as Cameron, dances ballet. In the second season's episodes "Allison From Palmdale" (season 2), Glau played Allison Young the human doppelganger of Cameron. Glau also guest starred in an episode of The Big Bang Theory, an CBS situation comedy.