A news show is broadcasting a persecution that is being followed by a reporter on a helicopter in Milwaukee, Wisconsin. Both cars collide. Suddenly, it looks like the reporter is in trouble, because there's something wrong with his eyes. A woman in the news studio is worried about him, she knows something is going on. The anchor woman asks him questions about the persecution but he says he can't see. The broadcast is interrupted. The helicopter has crashed.
Rachel and Jacob arrive at the scene. Rachel tells Hood they're waiting for a trainee, who has been assigned by the Director and will offer support in the investigation. His name is Felix Lee. Lee introduces himself. He tells them that the name of the pilot was Terry Gillman. He used to fly for the FBI. Apparently, he had saved the Director's life twice, explaining what Rachel and Hood are doing there. Terry was in perfect health. And he was also married.
Hood and Rachel visit Erica, Terry's wife. She says he loved his job. And that he wasn't even supposed to be working that night, but they called him in to cover the chase. She wants to know what happened to him. Hood tells him that Terry might have suffered something called rapid onset blindness, which is very rare. He wants to know if he had complain about his sight. Erica says no. She says her husband was so responsible that he wouldn't have flown if he'd had a problem. There's something else. She's pregnant. She never thought of raising a child on her own. She's very emotional. All she wants is her husband back. She asks Hood to tell her what happened. Hood promises her.
Hood is reviewing some of Terry's recent broadcasts to see if he finds any indication that he was sick. Debbie, another reporter, tells him that in the last 3 years all he had was a cold. She was Terry's assistant for a while. She's worried about Erica. The two were friends. Hood notices something. In one of the videos, Terry adjusted his head set several times, was scratching his neck and was sweating, even when the cabin was air conditioned. The day of that broadcast was two weeks ago. Debbie tells Hood she was the one to be told about him having a baby. Rachel gets a phone call. Erica is in the hospital. She's blind.
Hood and Rachel arrive at the hospital. They meet Dr. Nayar, who's in charge of Erica's case. He says she and the baby are doing fine. He's never seen anything like it, someone going blind all of a sudden. Other patients have arrived with strange symptoms such as lack of muscle coordination and skin rashes. Hood asks for specific cases. Dr. Nayar says a cop that was writing a ticket and had a rash; also a woman had numbness in her feet. They've been diagnosed with Burgers' disease. Hood says Minamata, a city in Japan where the first symptoms of metal poisoning were discovered. The doctor says they will run some more tests. Rachel wonders how people could be exposed to mercury in the city. Hood says they need to find out... before it ends up like Minamata.
A man is dumping some kind of waste into Upper Lake Park when he's surprised by Ben Finney, who is watching the area. The man gets a ticket for it.
Dr. Nayar tells Hood and Rachel that they found mercury in Erica Gillman and it was six times higher than the normal levels. The other patients had it too. But the doctor says it's treatable. Hood says it's good for the other patients but not for Erica. She can't be treated because the chemical used in the treatment in not safe for the baby. The problem is that the mercury is being passed to the baby through the placenta. The baby can have serious complications. The sooner they start the better. Dr. Nayar asks Erica for permission to perform an emergency C-section. Erica is worried because she's only in her second trimester and the baby won't survive. The doctor says there's a good chance the baby will. Erica wants a percentage of survival. Dr. Nayar explains every case is different, but Erica insists. The percentage is 10 to 15. Hood explains Erica that without intervention both her and the baby will get much sicker and the best way is to treat them separately. Erica says she lost her husband, but she won't lose her baby.
Rachel meets Hood in the hospital and tells him that they're bringing someone from EPA to help them in the investigation. Hood says that finding the source of the mercury will be very difficult. Rachel hopes that the mercury poisoning only stays in the 4 cases they have. Lee arrives and tells them that they've identified 25 more cases in the last 6 hours. Hood says they need to find the source immediately. Rachel asks if he has any ideas. Hood will try something called immersive garbology. Lee is excited, but has no idea what that is.
Apparently, immersive garbology is looking for any indication related to a case in garbage. Rachel thinks mercury was probably in something they ate or drank in large quantities. But that doesn't explain the other cases. Officer Barrett arrives at the scene. He's the traffic cop that had trouble writing tickets. He's there because they want to ask him if there was something her ate recently that they might find in the Gillman's garbage. As they go through it, Rachel shows him a carton of milk. He says he drinks it all the time. Hood runs a quick test on the milk. It's positive for mercury. Rachel orders Lee to call the Health Department. Rachel says they are able to take all the product from the stores but what about all the milk that has already been sold. Lee tells Rachel that they are two bottling plants and are shutting down their production. They will split up.
At the studio, Debbie is making a memorial video for Terry. The man we previously saw at the lake writing a ticket, is Debbie's husband. She tells him that she'll be done with that video about pollution he asked her. He says not to worry. Terry's video is more important. He wishes there was something he could do. Debbie just misses her friend.
Agent Lee is at one of the bottling plants and calls Rachel. He tells her that the equipment of the plant is clean but some of milk has tested positive for mercury, however, it's not coming from that plant. The plant Rachel and Hood checked was clean too. Maybe the milk was tainted before. Hood thinks it comes from the dairy farms. They find out that there are more than 20. Lee finds out in the database that only one supplies fresh milk to both plants.
Finney arrives at a place where they sell junk and buys an old refrigerator.
Hood and Rachel visit Endora dairy farm. The owner tells them his cattle is healthy. Hood says the farm is way too big for the amount of cattle he owns. He wonders where the rest is. The man says he's sold the rest. Hood takes a look at the field in front of the farm. He asks the man if he's thinking of expanding his dairy, because it looks like the field has been leveled. Hood asks Rachel to call Lee. He helps dig up a dead cow.
Lee talks to the farm owner. He says that he understands him, since he actually comes from a farm. He did what he had to do. The man says the cows were losing weight and he thought they had mad cow disease. He got scared so he euthanized them. Hood informs him that the cows didn't have the disease, they had mercury in their systems which went directly to the milk. The man says he couldn't know that. But Rachel tells them he knew they were sick and he should've called for help, but instead he just covered it up. He defends himself saying that he was protecting his livelihood and his family. Hood asks him to think about the families who drank the milk. The man won't say anything else, he wants a lawyer. Rachel says he'll need one. He's taken into custody. Hood says that now he knows how the mercury got to the milk, now they need to find out how it got to the cattle.
Back at the hospital, Dr. Nayar is checking Erica's baby through an ultrasound. He says its heart and lungs are developing normally, but he's worried about her heart. The longer she waits for the treatment the more the stress she will put in her vital organs. The doctor says that he doesn't want to lose both. Erica says that the baby is fine. Dr. Nayar tells her that he can't know how the mercury is affecting him. Erica is surprised the doctor referred to the baby as "him". It's a boy.
Back at the dairy farm, Hood gets a phone call from the head of Obstetrics at Johns Hopkins. He was trying to get some help for Erica and her baby. But it didn't work out. Lee asks Hood how he deals with people who have lost so much. Hood says he hasn't worked that one out yet. Rachel joins them and says that the rest of the cattle is clean, so Hood thinks they ate or drank something the others didn't. Checking their stomachs' contents will take time. Rachel wonders if there is a way to find out faster. Hood says there is. Rachel's worried they'll go back to go through garbage. Hood says there's no need to, because she's standing right on it.
Hood is analyzing the cows' feces when he finds fish bones in it. Rachel says she thought cows were vegetarian, however Hood says many farmers give them meat as supplement and the cheapest is fish. Rachel will investigate the distributors.
Lee finds the meal source. Hood and Rachel are at the lake. Hood tells her that there are only some fish that can carry dangerous levels of mercury like swordfish and shark. Rachel doubts there are those kind of fish in a lake. Hood says mercury must've found its way into little fish. Rachel says that the lake is huge and she doubts they can search all of it. Hood spots a seagull. The seagull has some tracking device attached to its leg. They both drive near the lake. Hood says that seagulls eat anything, so if they are poisoned with mercury they will notice something like violent behavior. As he mentions this several seagulls crash into the windshield and windows. Rachel drives back. As they get out of the car, Ben Finney meets them. He asks them if they're both OK. Hood tells Rachel they need to get to the source before it turns up somewhere else.
Finney and Hood are analyzing a dead seagull. Hood asks Finney how long he's been with the department of fish and wildlife. Finney says enough to see so many species go extinct. He also says that there's so much evidence that we're killing our planet, but it will take a while before the government notices. Rachel tells him they're not the enemy. Finney takes the device from the animal and tells Hood that they use the device for the birds' breeding and migratory patterns. Hood tells Rachel that will lead them to the source.
Rachel and Hood take a ride on a boat to an area given away by the GPS on the seagull's transmitter. And they will find any debris at the bottom of the lake with some sort of radar. Something comes up on the screen. Divers go down the bottom of the lake. They take out an old refrigerator. Lee opens it. Lots of mercury come out of it. They find a barometer. Lee says that old barometers had mercury. Rachel thinks that wasn't an accident. Hood says he knows a way to find who did that. Mercury is dangerous, so if you want to buy that much without a license, you can do it paying cash to someone who doesn't ask many questions. Lee is impressed by their brainstorming. Rachel asks him to get every field agent canvass every antique shop near the area. Hood gets a phone call from the hospital. It's Erica.
Dr. Nayar tells them Erica had a seizure. And she won't give her consent to deliver the baby. Hood says she's facing the toughest decision of her life. And Rachel says she can't even tell her husband about it.
Erica learns her baby is suffering. If she doesn't induce, he will die. She's very confused, she doesn't know what to do. She asks Hood what he would do, if it was his wife. He tells her, that if it were his wife, he'd say to hell with the science, follow your heart. Rachel is looking at them from outside.
Debbie arrives and asks how's Erica. Hood comes out of the room with good news, she's having the baby. Rachel leaves to tell Dr. Nayar. Now they have to wait. Lee arrives as well. He found out that local antique shops sold more than 30 barometers in the last 6 weeks. One of the shops gave him a name, Larus Saundersi. That person asked to be called if more barometers came in. Number was traced back to a disposable cell phone and the name doesn't exist. Debbie hears the conversation and tells Lee the name does exist. Larus Saundersi is the Latin name for the Saunders gull, an endangered species. Hood notices the necklace Debbie is wearing. It's beginning to oxidize. He asks her if anyone who has touched it has been handling mercury. Maybe someone who works for the department of fish and wildlife. Debbie says her husband, and he gave her that necklace a week ago.
Debbie meets Finney at the lake. He says she shouldn't be there. She wants to know what he's doing. She wants him to tell her that he didn't poison all those people. Finney says he just wanted their attention. Debbie is shocked. She tells him Terry died and his wife and baby are in danger. He didn't mean to do that. He did it for them, for the baby they will have someday and their children too. He says he's the only one that cares about that place and no one else. He tells her that she's the one telling him that people only seem to take notice when something bad happens. It's front page news. She gives him the necklace back. She leaves. He wants to explain but Rachel comes out and tells him he will come with them. Finney tells her that when there are no fish and no trees, she'll regret stopping him. Rachel says he killed someone. And she's not sorry. He tries to escape but Lee stops him. He's placed under arrest.
At the hospital, Erica is watching her baby at an incubator. The baby is strong, like his mom, Hood says.
Lee is waiting for Hood and Rachel. The case is closed and Hood thanks him for his help. So that's it. Lee is saying goodbye to both Hood and Rachel, when he asks if he could stick around. He says, however, that other people have expressed interest in his work. Rachel says that's weird because she spoke to the Director and he told her that he had begged for that assignment. Lee is embarrassed. But he says that to be honest, the work Hood and Rachel do is awesome. Rachel smiles, Hood thanks him. Lee just had to see for himself. Hood asks Rachel for her opinion but she says it's his call. Hood asks Lee if he will not make him regret his decision. He says no and he hugs Hood. They will be like the 3 Musketeers.