The younger sister of Timothy Murphy, and the granddaughter of John Hammond, Lex Murphy was invited to Jurassic Park by Hammond to keep the park from being closed by Donald Gennaro. Lex accompanied the adults on the tour of Jurassic Park. However, she was uninterested by the dinosaurs, preferring to play catch or talk about baseball. She was the original person to spot the Velociraptors stowed-away on the supply boat. Later, she was among those in the Land Cruisers attacked by the Tyrannosaurus rex. She survived the attack with minimal injuries, and traveled with Alan Grant and Tim to reach safety. They stayed in a feeding structure for a night, and made friends with a baby Triceratops she named Ralph. She also survived a stampede of Maiasaura escaping from the adult Tyrannosaurus.
When Grant was able to secure a raft and allow them to travel to the Visitors Center by water, Lex accidentally interrupted the nearby sleeping Tyrannosaurus and initiated an attack. They were only saved when the juvenile rex distracted the adult. Lex was also attacked by one of the Cearadactylus in the Aviary and lost her baseball mitt, and later by a small pack of Velociraptors in the Visitors Center. She survived both ordeals, and unexpectedly helped Tim restart the park systems. She was rescued by helicopter and flown off the island.