In Virginia a young woman is attacked by an invincible brain-eating monster that threatens to take her life. A Midwestern farmer does battle with a beast that cannot be killed and a New Yorker is infected with the deadliest parasite on the planet. Three parasites that are almost impossible to destroy; three victims, fighting for their lives. If doctors cannot cure them their only hope of survival is by living with the enemy inside them.

Nature is a war zone and parasites are the ultimate fighters. They are hungry, they are ruthless and they don't play by the rules. Parasites have evolved countless ways of hijacking their hosts' bodies: some steal food from inside the gut, others lurk in the blood sapping their host's nutrients and some even target their host's brain. These are some of the most horrific cases of parasitic infection in the United States. In Virginia a vicious creature is on the rampage, its next victim is an innocent child. In Michigan a brutal killer has invaded a traveler's blood, and a summer's day at a Florida lake turns into a nightmare when a ruthless monster attacks a young boy's brain.

Parasites are ruthless, single-minded and above all devious. To become the most prolific life forms in the world takes a degree of cunning that others can only marvel at. Meet the most deceptive parasites on the planet, the "Masters of Disguise." Teenager Mallorie Greiner has Acanthamoeba keratitis, a parasite that's intent on eating her cornea. Doctors are bewildered at first because her symptoms look just like herpes. Runner Rick DiMichele is struck down with a debilitating disease. Initially, doctors think it's cancer, then malaria; eventually, they discover he has a tick-borne disease called Babesiosis. And not until he's staring death in the face do Mohammed Meah's doctors find the real cause of his problem: a parasitic worm called Strongyloides that's been lurking undetected in his small intestine and living off the steroids he was taking to combat his colitis.

Perfecting the art of reproduction have made parasites the most successful life form on the planet. There are some who are violent, manipulative and have taken sex to the extreme. These parasites are sex maniacs. A New Jersey woman finds her apartment infested with one of the most ubiquitous parasites on earth — bed bugs. Part of the reason for their success is the males' aggressive approach to sex, a method known as "traumatic insemination." A cyclist from Colorado discovers that the insect bites on his head are from botflies. In Oklahoma, a chemical sprayer's cough turns out to be the result of parasitic worms that multiply in the human lung.

Across the United States, doctors and scientists are fighting a war against some of nature's deadliest creatures — parasites. It is a race against time when a mysterious organism strikes a mid-western city causing the worst parasitic outbreak in the history of the United States. Before the culprit is contained, 100 innocent people have died. In Chicago, doctors must track down a hidden killer that attacks a group of students on a spring break trip, and a flesh-eating monster is on the loose in a Texas community.

These killers lie dormant, waiting for the right time to strike. Eleven-month-old Garrett Richardson ingests the eggs of a worm, and within days the creature travels to his brain and goes about feeding on its tissue. A Vietnam veteran survived the enemy attacks on the front lines, but back at home — unknown to him — a killer is stealthily working its way through his body, laying waste to his organs and lymph system. By the time the medical evidence reveals the source many years later, the killer is long gone. And John Figge and many of his family members live for six years with unwanted hitchhikers from Africa traveling around in their bodies. Only when one of these creatures begins to attack John's brain are they discovered. Can the family get rid of these deadly parasites before the damage is critical? These are all stealthy predators that get inside their hosts, yet work on very different timetables. Dangerous and often hard to detect, this is the story of the war on sleeper cell parasites.