The BAU flies to LA when the cops discover an unusual string of murders - overweight women who were drowned and then dumped all over town. Even odder, each body has a small chunk of flesh removed from their feet.
The team seems to have a lead when they learn that the victims were drowned in methanol, a highly toxic wood alcohol that dissolves chemical bonds at the molecular level. Unfortunately, Reid learns that the substance is used quite often in manufacturing - tracing it to the killer is impossible. The team instead focuses in on how the killer lures and disposes of his victims, eventually coming to the correct assumption that their UnSub is a taxi driver.
When the UnSub kidnaps yet another woman, the team attempts to hone in on the killer before it's too late. They hold a press conference in the hopes that someone came into contact with their UnSub and survived. They find a woman, Bailey, who had been kicked out of the UnSub's taxi earlier for putting on perfume. This is the last piece of the puzzle that our team needed to figure out what was triggering this UnSub's psychosis: scent. We learn that the driver is a twisted sort of scientist, and the chunks he took out of his victims' feet were samples. He is obsessed with smell, and has been kidnapping women in order to chemically distill their scent essences into candles.
Using the information they got from Bailey about the UnSub's taxi, they track him to his garage. They manage to save Anisa in the nick of time, but the UnSub escapes in his taxi. A long car chase ensues, ending in the UnSub's death.
Meanwhile, we learn more about Prentiss' mysterious past as a special agent catching terrorists in Europe.