Grissom investigates a murdered jogger while Catherine looks into a death at a carnival.
Tropes:
- Conviction by Counterfactual Clue: Catherine realizes that the mother is lying... based on her eye movements while they talked. Especially frustrating because she has just proved that the daughter couldn't have been killed by anyone else with solid enough physical evidence.
- I'm a Humanitarian: Susan keeps herself young and beautiful by drinking protein shakes made of ground-up human livers. She offers one of the shakes to Grissom at the end of the episode. Grissom called her out on how untreated porphyria also causes psychological disorders, implying that she only thought it was her diet that kept her beautiful.
- Looks Worth Killing For: Susan eats other people's organs so that she won't be disfigured by her porphyria (it's left ambiguous as to whether it makes any difference). It's made clear that she's using it to preserve her looks rather than her health.
- Mad Doctor: Susan Hillridge is a mad nutritionist. She has a bad case of porphyria and thinks that the best way to stave off its symptoms is to feast on the most blood-rich organs of healthy men.
- Motive Misidentification: Grissom and Nick initially assume that Susan is stealing organs to sell them. She's actually eating them.
- Organ Theft: Organ-legging is mentioned, as the murdered jogger has had his liver and a couple other organs removed. At the end of the episode, it turns out that the killer took the most blood-rich organs to make into a health elixir, convinced that it's the only thing preventing her from becoming sick.
- Our Vampires Are Different: Susan is a nutritionist with porphyria
who liquifies human organs and drinks them to get the enzymes she needs. Interestingly, porphyria is often cited as a possible influence for the creation of vampire myths, as the symptoms of some forms of it can mimic vampire traits; extreme pallor and sensitivity to light, receding gums which make the teeth appear longer, mental disturbances such as paranoia and hallucinations, etc. However, since vamps being harmed by sunlight is a recent invention, this speculation is questioned just as often. - Picky People Eater: Susan has her attack dogs kill people, then converts the most blood-rich of their internal organs into a milkshake-like slurry. She suffers from porphyria, a metabolic disorder that caused insanity in her case, and is convinced that consuming such organs is the only way for her to self-medicate.
- "The Reason You Suck" Speech: Catherine calls out the mother as she's leaving the precinct when she learns that the woman killed her own daughter so she'd be free to run off with her boyfriend. It ends with the mother asking for a lawyer.
- Serial Killer: Susan Hillridge is one of the first one-off serial killers in the series.
- Soft-Spoken Sadist: Susan's voice never raises an octave.
- Tunnel of Love: The mother uses the darkness of a Tunnel of Love ride at a travelling carnival as cover to drown her daughter, hoping to pass the girl's death off as an accident due to a seatbelt being too loose, and accuses the carnival of negligence.
