WILLIMET, MARYLAND – Two teenagers are in a car at night, making out. The boy starts to turn the car to return the way they came but the car stalls in the middle of the road. The girl sees a car coming fast toward them. The boy can't start the car so covers his girlfriend, anticipating the crash. But at the last moment, the other car swerves and crashes. The teens go to the car and find the driver, Clayton Beyer, obviously sick who tells them to look after his sick daughter, Carla, in the back of the car…
Two days later, Connor briefs the team at NIH. 4 deaths in one town. It is Aplastic Anaemia which destroys bone marrow which means no blood cells, no oxygen, no immunity to disease and no blood clotting. This is a rare but very deadly disease and this kind of cluster is very alarming. Frank lists the causes of it: toxic exposure, drugs and medications, radiation exposure and viral infection. So far the four who've died have no ties, no exposure, no commonalities. Durant adds that the blood and tissue degradation has made the bodies useless for answers. The disease isn't contagious but it is spreading. What they need is a living victim… Eva runs in, there's a new case, Carla, and she's alive.
The team goes to Willimet. Carla will need a bone marrow transplant, Connor says see if the father is a match. Unfortunately, the father also died of the same thing, and the police have been unable to find Carla's mother, they're not even sure of her name. Frank and Eva go to the father's house and discover it is extremely neat and orderly, he was a CPA. They find a calendar that says that Carla visited her mother the entire previous week so they check phone records, assuming that the father would have keep in regular contact while she was there. They get her name, Angela Beyers, who lives in Willimet, in the original cluster of four infected.
Durant and Connor go to the mother's apartment but it is located in a slum, graffiti on the walls etc. When there is no answer, Connor kicks the door in. At Durant's astonished look, Connor says it's an emergency. They find the mother but she's been dead for days. Eva and Frank meet them there. Durant quickly rules out Aplastic Anaemia as the cause and Frank finds a dirty needle, she was an addict. They find payslips from a bar and wonder if that could be the source of the disease. They find medication which indicates Angela had Hepatitis, a type of which can cause Aplastic Anaemia. Eva suggests that maybe Carla caught it from her mother. Connor issues orders – Durant: get the mother and father to NIH for autopsy ; Eva: dig into their backgrounds, find a relative who could be a donor ; Frank: find out if any of the first four victims visited the bar Angela worked at.
Frank talks to the bar owner who doesn't recognize any of the photos. Connor orders Carla in a reverse isolation unit at NIH, intended to keep what's outside out, with her immune system failing, she must be protected from everything. Eva reports that Carla's parents have no living family, Carla is completely alone. Miles suggests a blood transfusion, it might make her strong enough to wake up so they can question her. Connor says not yet, it increases the chances of Carla's body rejecting a bone marrow transplant.
Durant reports the mother died of liver failure due to the Hepatitus C, a strain which does not cause Aplastic Anaemia. But Durant did find something useful – Clayton and Angela are not Carla's biological parents. If they can find their birth parents, maybe they can find her a donor. Eva and Frank return to the father's house and find a payment to an agency. They go to the agency and explain what's happened but the woman refuses to help them. Legally, she needs a court order to release the records. Eva makes an emotional appeal but the woman still refuses. The Bone Marrow Registry turns up no compatible donors but Durant reports two new cases, a retired building contractor and a college student, both before the other four cases.
Eva calls in a favor with an old friend and gets the court order in record time and slaps it down on the woman's table. Eva and Connor drive to Carla's biological mother's house. Her name in Cyndi Weaver, no father listed and she ticked the box on the form saying she never wanted contact with her child ever. They interrupt a birthday party, Cyndi is married with two young sons. When they explain why they are there, she goes cold and denies knowing what they're talking about, all but slamming the door in their faces. But she had been blowing up a balloon when she came to the door and dropped it, which Eva intends to take to the lab to prove she's Carla's mother. Eva sits with Carla and tells Connor that at ten, Carla won't get adopted, she'll end up in the foster care system. The DNA test comes back and is positive, Cyndi's Carla's mother, and Eva swears to get Cyndi to come.
Miles suggests the blood transfusion again and Frank agrees with Miles – they've got nothing else. Connor reluctantly agrees. Eva waits till Cyndi's husband takes their sons to school before going to stand behind Cyndi's car to stop her leaving. Cyndi reluctantly lets Eva into her house and Eva tries hard to sympathize with her and reason with her. But in the end, Cyndi is too afraid of losing all she's built and refuses.
Miles tells Connor and Durant that Carla's waking up. Connor doesn't tell her about her parents being dead. After some questioning, Carla mentions she and her parents had a picnic by the river and she and her father went swimming in it. Connor sends Frank to investigate. Frank talks to the widow of one of the victims, a retired contractor, who fished regularly in the same river. The wife mentions 'dirty water', mentioning the chemical plant up the river which has been cited by the EPA for dumping Benzine in the river. Frank checks and finds out the college student was a water-ski instructor. Connor calls Durant and tells her to check the victims for Benzine.
Carla goes into defib but they manage to get her back. Just then, Eva returns to tell Connor that she has failed. Durant's tests don't turn up Benzine but another chemical in all their systems which does cause Aplastic Anaemia. It's a powerful antibiotic to keep animals healthy, used in foreign countries and it's illegal to import foodstuffs containing it. Chicken, crayfish, shrimp etc. Frank remembers the contractor, he had undigested shrimp in his stomach. Frank returns to the contractor's wife who says that her husband loved shrimp, ate it almost every day but she doesn't know where he got it.
Cyndi shows up at Eva's office. She told her husband she's visiting a friend for the weekend, she'll help but she has one condition – she doesn't want to see Carla or for Carla to see her. Connor immediately agrees. Durant harvests the bone marrow, then prepares to transplant it into Carla who has an allergic reaction. Durant wants to stop the procedure but Connor insists she continues – Carla will die without it, they'll treat the allergic reaction separately.
Frank returns to the bar owner and asks if he knows if Angela took shrimp for the picnic. The bar owner says yes, she took the leftovers from the day before. Frank gets the name of the supplier and tells the bar owner to dump whatever shrimp he has left.
Connor, Durant, Eva and Miles wait outside Carla's room. Frank arrives with good news, the shrimp came from Vietnam imports and the importer has been shut down. Carla wakes up and announces she's hungry. When she asks where her parents are, Connor is left alone with her to explain.
Eva sees Cyndi leaving and Cyndi hesitantly asks if Carla's alright. Eva won't answer, instead telling her to look for herself, which she does, beginning to cry. Carla is awake and sees her but doesn't know who she is.
Connor visits Eva and he asks her about her own birth mother, Eva was given up for adoption. Eva just says that when she went looking for her, that her mother didn't answer the door.