A young girl is brought to the hospital with stabbing pains in her scalp; a mother's mysterious symptoms threaten to tear a family apart; a deadly invader turns a relaxing vacation into a nightmare.

A man falls comatose; a college student has a sore throat; and a young woman's symptoms confound experts.

A man has something living in his eye; a young girl mysteriously falls ill; and a woman's bizarre symptoms push her to the brink of insanity.

An infant falls mysteriously ill; a biology professor becomes an unexpected host; and a family man is brought to the brink.

A new mother is in critical condition; a young boy has an ailment that no antibiotics can cure; and a young man has an invader in his brain.

A young boy has a strange condition; a woman's symptoms push her to madness; and a toddler falls into a trance-like state when something begins eating his brain.

A teenager develops mysterious blotchy sores; an athlete is hit by a rare infection; and a woman battles strange bouts of vomiting.

A man coughs up blood; a newlywed husband is struck down by a rare disease; and a father struggles with abdominal pain.

An infant is suddenly paralyzed; a father is infected with a monster that threatens to blind him; and a woman's excruciating pain confounds doctors.

A woman is struck down by a dangerous parasite; an infant falls mysterious ill; and a fungus brings a young man to the brink of death.

After a man hits his head, he's left fighting a one-on-a-million medical mystery; a boy's wounded knee becomes home to an uninvited guest; a man unwittingly feeds his own intended killer.

A man develops a strange growth on his wrist; a nurse finds twig-like pieces in her urine; and a pregnant woman falls ill with flu-like symptoms.

Christmas time is here, and these three victims each receive a monstrous gift. In Florida, a woman is out Christmas shopping when she suddenly feels a stabbing pain in her eye so severe that she believes she sees shadows of worms in her eye.