A 4-year-old boy literally drowns in his own mucus, being a victim of an outbreak of the Enterovirus D68 virus; a 7-year old scrapes his knee on a rock at the beach, but when his father puts a liquid bandage on it, it causes it to swell the size of an orange – then, his mother squeezes the wound and finds a sea snail (Littorina scutulata) inside; a college student experiences loss of appetite, fatigue, fever, jaundice, and repetitive nightmares that turn into a reality from getting infected with malaria caused by the Plasmodium falciparum parasite after returning from a trip to Ghana.

An athlete gets headaches, stomach pains, breathing difficulties, and a liver mass from Entamoeba histolytica from a trip to Nicaragua; a teenager develops a leg welt and then gets fatigue and red spots on his body over the course of several years. When the spots open, the doctors discover he has leprosy from coming into contact with an infected nine-banded armadillo (Dasypus novemcinctus). A woman suffers severe headaches, nausea, vomiting, and seizures from Exserohilum rostratum fungi invading her brain.

During a fishing vacation, a soccer coach goes into septic shock from Vibrio vulnificus necrotizing fasciitis after banging his ankle on a barnacle; a 7-year-old girl gets facial tics, bouts of anxiety, and turns suicidal after a streptococcal brain infection; a makeup artist gets severe stomach cramps and watery diarrhea from Giardia lamblia.

A newlywed woman gets extreme headaches, memory problems, sinus pressure, and painful rashes, while her husband gets endless nosebleeds, breathing problems, and brain fog, both from Aspergillus; a councilman loses his spleen to visceral leishmaniasis; a 6-year-old gets a fever, red spots, a swollen mouth, loss of appetite, leg weakness, and breathing difficulties from rat bite fever caused by Streptobacillus moniliformis.

An 11-month-old boy experiences wheezing and vomiting after swallowing a button battery; a landscaper becomes infected with Paragonimus kellicotti; a female boxer gets a severe headache, a 105 fever, and impaired vision from cat scratch fever caused by Bartonella henselae.

A 2-year-old girl experiences severe pain, trouble breathing, and vomiting from a bark scorpion sting; a neuroscientist experiences multi-organ failure and nearly dies from a leptospirosis infection that he caught while swimming in Hawaii; a 20-year-old woman suffers from severe vomiting, extreme headaches, twitching and a strange crawling sensation in her head that turns out to be caused by Balamuthia mandrillaris and dies from it.

A young college student contracts Acanthamoeba keratitis from sleeping in her contact lenses; an infant becomes temporarily paralyzed and almost dies from accidental ingestion of soil that contained the most deadly toxin known to science, botulinum toxin. A new mother has extreme pain from a piece of gauze that was left inside her abdomen during a C-section.

A California teenager nearly suffocates from hantavirus pulmonary syndrome; a Hawaiian personal trainer suffers years of excruciating neuropathic pain from ciguatera poisoning caused by Gambierdiscus toxicus toxins; a Michigan health worker nearly dies from babesiosis.

A 13-year-old boy gets a cut on his leg that nearly leads to amputation when it becomes infected with Staphylococcus aureus, causing necrotizing fasciitis; a couple move into their new home, but over the course of three years, the man suffers a spreading/oozing rash, poor coordination, body aches, breathing difficulties, and weight loss, while his girlfriend suffers memory loss, fatigue, and suicidal depression, both from chronic low grade carbon monoxide poisoning; an 8-year-old girl from Hawaii gets a growing mass in her eye from Toxocara canis.

The third episode of the series to be Christmas-themed – A baby is having problems controlling the left side of her body, along with multiple miniature seizures before doctors discover the right side of her brain is malformed due to a Cytomegalovirus infection; a PR executive suffers a year-long ailment that turns out to be a cyst caused by Echinococcus granulosus tapeworms infecting her spleen; seizures ruin a schoolteacher's Thanksgiving, and when they worsen around Christmas, doctors discover a pork tapeworm cyst.