Isabel Evans is an alien-human hybrid like her brother Max Evans and best friend Michael Guerin. She and Max were found as six-year-old children wandering in the desert by Philip and Diane Evans, who adopted them. She had a relationship with Alex Whitman in season one and again in season two, but the relationship never really got off the ground in season one before her "destiny" was revealed. Just as she and Alex started over in season two, Alex was killed. She was devastated by Alex's death, having a couple of dreams about him (one in which she admitted she loved him), but moved on to marry Jesse Ramirez in season three. She and her mother shared a close relationship, although it was strained when Isabel decided to marry Jesse. Over the years, Isabel's relationships with Max and Michael were also put under pressure. She became notably good friends with Kyle Valenti and saw Sheriff Jim Valenti as a father figure.

Isabel is a very visible, popular girl at school. She hides her kind side beneath a front of haughtiness and cold unfeeling—she is the perfect, unknowable, unobtainable beauty. On the outside, she is the most outgoing of the three hybrids and blends in with the human society with ease. While Michael is a rebellious loner and Max is shy and quiet, she is an active participant in social activities and very confident. However, deep down she craves stability and security, longing to fit in and be a "normal" girl like Liz or Maria.