Jessie is very adventurous and loves to explore. She enjoys learning about creation, from more of a country perspective, rather than the technological way of things. She is homeschooled and is very bright, as well as being described as having a lot of "spunk". In her early years she was easily excited and a bit out of control, but as she grew older she mellowed out and became a faithful helper to her father, Jim Brenan.
Jessie and her family met Jonathan and Kendall in the cave, where they took shelter from the storm. At first Jessie was worried about her pets, but after meeting Jonathan and hearing his story, she quickly befriended the lonely boy and explored the cave with him. After narrowly escaping a pit, the two children found a dinosaur skull and showed it to Kendall, before leaving the Cave.
Jessie and the Brenans returned home, where their land was a disaster and their livelihood destroyed. Jessie was horrified to learn that her pet cow was missing. Then Simon Addlemanand his henchmen burned their barn to the ground, and Jessie narrowly avoided being burned. She, Jonathan, and Kendal returned to the cave and ran into Simon Addleman, who threatened to hurt Jonathan and Jessie if he didn't get the skull. The children outwitted him and left the cave with the skull.
Later Jessie and her family go on vacation to Florida. After being followed by the Parks, Jessie joins them in their expedition and helps Jonathan make the right choice about Billy. In Disaster at Brenan Bluff Jessie is trapped by a falling stone and counsels Jonathan through his pride. The Parks and Brenans have several adventures after that. Then Simon, Marvin, and Vinnie return to the cave to hide computer chips. Jessie and Jonathan face him again and save him when he falls, even though he's been horrible to them and their families.
Jessie is best friends with Jonathan Park and Katie Park. At first she and Jonathan were reluctant friends, but after a few adventures became inseparable. After the CRT was formed, she was paired with Katie as one of their researchers.
Jessie is the daughter of Jim Brenan and Martha Brenan and sister to Ryan Brenan and Summer Melody Brenan. She is very close to her parents and obeys them. Jessie is particularly close to her father, becoming his personal assistant and encourager in The Copper Scroll. She doesn't spend much time with Ryan, her little brother, but she loves him and her sister deeply.
Jonathan: "That was close. I thought I was about to lose my only..." Jessie: "...Friend? Jonathan Park! Were you about to call me a friend? Admit it! We were starting to become friends." Jonathan: "I'm not admitting nothing."
- Unlike the boys, Jessie has been played by one actor throughout the entire series.
- In Mystery at Dead Man's Curve, she appears to be a member of the Eagle's Nest Gang, but she is not at any of their meetings.
- Jessie has a soft spot for animals thanks to her farm upbringing. This sometimes gets her into trouble, like in The Ancient City of the Jaguar, where she lost her purse to a monkey.
- In the reboot of the series, Jessie appears in pants and a jacket. In the album art before this No Looking Back, she wears a shirt and a skirt.
Main article: Jessie Brenan/Gallery