Part horror movie, part medical detective story, find out what happens when people fall prey to an infection from a parasite, those nasty microscopic creatures found in water, soil and even in the air. Victims' stories are retold, including how doctors and scientists attempt to unravel each case before it's too late. Biologist Dan Riskin, assisted by doctors and experts who witnessed each case, leads the scientific discussion about each parasite.

A team of experts, including biologist Dan Riskin, zoologist Lucy Cooke, wildlife expert Bradley Trevor Greive and marine biologist Andrew Nosal, unpack nature's strangest mysteries to reveal the explanations behind these remarkable behaviors.