A woman takes a vitamin pill before heading to work, only she dies before she can get there. During the autopsy Dr. Graf determines she died of a heart attack. Marc questions the firm who makes the drug but they deny any money demands, but Marc and Niki think they are hiding something.

A series of death along with Danube lead Marc to think a crocodile is responsible, but is it really? During an autopsy Dr. Graf confirms that the latest victim did indeed drown. Still puzzled, Rex's finds some new evidence, which turns the case around.