The body of an unknown young man pronounced dead on the Las Vegas strip walked out of the coroner's before he was autopsied. Not long after another young man's body was discovered, but got up and walked away from the crime scene. Evidence pulled from the first body led the CSIs to an old government research program run by Dr. Elliot Davis Aden at a local University.
Three students from the university were attempting to duplicate Dr. Aden's experiments into the beyond. The CSIs learned that the zombie like state was produced by a neurotoxin that acted as a paralytic. The toxin was taken with psychedelic drugs meant to enhance the feeling of crossing over into death. One of the students was found drowned in a sensory deprivation chamber and another was found in the cemetery still under the effects of the drugs. He ran from the police and was killed by a car.
After reviewing another notebook full of Dr. Aden's notes the CSIs discovered that the doctor was still conducting his research and used the three students to collect more data. Dr. Aden left a video recording stating that it was time for him to crossover himself and was found in a paralyzed state. The third student was eventually found back at the university alive, and unaware of what had happened to the others.