David's dad Having lost his house in a fire, David is taking him to a seniors' residence. Arguing along the way, they arrive, Toumas is very critical of his new surroundings. He refers to it as a brick box, soulless and unattractive. David tells his father that his things will be there in a couple of days, and it'll be just like home. Toumas tells him that he has Alzheimer's, he was diagnosed a few weeks before Lydia died. David takes his leave of his father, telling him "Welcome to Toronto". David imagines himself asking his father to stay with him, but instead turns and leaves.
At Norbac, David pulls into his parking spot and parks when suddenly a dead fish lands on his windshield. Swearing, he gets out of the car to confront a fisherman, who tells him his family has been eating genetically modified fish for almost three years. The fisherman is Earl Jordan, and he's been emailing David, asking about the fish, and why David deemed it safe. Earl's son is paralyzed, and Earl believes it's because his wife ate the fish while she was pregnant. All tests on his son have come back with no results, and Earl believes it's David's fault for declaring the fish safe. He's brought his son's samples, charts and documents, asking David to have a look at them, see if he can figure out what's wrong with him. Earl leaves, apologizing for the windshield stunt, and David turns to go in the building, leaving the box of samples on the steps, but turns around, swearing, and picks up the box to take it inside.
David sees Jill back at work, as she was let out of the hospital earlier that day. David bought her a brand new vortex as a "welcome back" present, and he got her an advance copy of an Italian study on retroviruses. Jill is ecstatic with both gifts, and impulsively kisses him before leaving to go read the study.
Caroline is on the phone filling in Connor about the worms, which they think came from Haiti on the winds of Hurricane Katrina. She tells him that they are optimistic about treatment, when Connor puts her on hold. David pops in at that moment to let Caroline know he needs to "buy a new pencil" - in other words, do some independent research using the lab's facilities - and Caroline, distracted, says that they'll talk later. David takes that as an approval and heads back out the door just as Connor comes back on the line, causing Caroline to have to leave the situation as is. She agrees to come to Washington to meet with the Appropriations Committee, whose head is from Arkansas.
David goes back down to his car to get the fish that Earl had tossed on it, and runs into Mayko and Bob on the way back in. Mayko can't resist the fish jokes, and David tells her to go look up any public health studies done lately on GMO fish. He then tells Bob he needs to use his station, and when Bob asks why, David gestures with the fish. He tells Bob that he wants to make sure that this fish is the same GMO as what was approved by that panel. He then passes Bob the vial of blood from Earl's son to have him check the DNA, see if there is anything wrong with it. Bob tells him he's feeling guilty, which is good because that's when he does his best work.
David processes samples from the fish, while Bob works with the blood sample. Bob tells David, Carlos and Mayko over dinner that part of the little boy's DNA is turned backwards, which could be a genetic abnormality, or it could be from the fish, or any number of things. David says the fish that he checked had the modification that was supposed to be there - a modification of the gene that produces the growth hormone so the fish grow larger. There's a knock on the door - Jill has arrived for her welcome home dinner, along with an unannounced guest, Toumas. The discussion over dinner is about GMO's and is understandably heated. Toumas effectively ends it by saying that people are the guinea pigs in the largest experiment ever undertaken, to which David replies that of course, it is all just a grand conspiracy. He leaves the table, at which point Mayko asks Toumas what David was like as a child. Toumas tells them that David was brilliant, and arrogant, and that he got it all from his father. He then asks Mayko how long she and David have been married, stunning the table into silence.
The next day, David calls Earl to tell him that they haven't found anything in the GMO fish. He tells him that they did find a genetic irregularity in Earl's son's blood, and that they are continuing to look into it. Mayko makes some phone calls, looking for other children who exhibit the same kind of symptoms, although none actually match the type or severity of Earl's son. All are clustered around the same peninsula, though, so David says he needs medical records and DNA samples from the families involved. Mayko tells him that she asked for food samples as well, which is predominantly seafood.
In Washington, Connor escorts Caroline into his office, and tells her that a National Guard unit in Ohio was doing a routine endurance course when they all came down with the same symptoms - thirty people, in total. Apparently Homeland Security is hearing threats that Al Qaeda is going to attack in heartland America, and there is belief that there is a cell located in the area.
At the lab, Wes is attempting to get Jill to sign a release, stating that Norbac is not responsible for her accident. Jill refuses, saying that it was not an accident. David, hearing part of this, asks Jill if everything is okay, and she says it's fine. He reminds her of the meeting, and leaves. Jill reiterates that it was not an accident, and Wes tells her it doesn't matter, he just needs her to sign the form. Jill refuses, telling Wes she'll sign the forms when he starts doing his job - find out why research goes missing, who messed with her lab equipment, then leaves for the conference room.
Mayko tells everyone that they're looking at a group of kids with muscle development problems, and hands out the information. Carlos is looking at DNA profiles on the fish samples, Bob and Jill are going to analyze the fish for toxins, and Mayko is going to contact an epidemiologist. David says he has some catching up to do, and goes to his office to lie down. Caroline phones, and tells him to get to Downsview - there's a military plane waiting for him. When he asks her where he's going, she says she can't tell him.
David and Caroline arrive at the National Guard facility in Ohio, where there is a full quarantine in effect for the soldiers affected. Of the thirty two soldiers in the unit, thirty are sick, and two are AWOL. The base doctor tells them that they've done everything they can, but nothing has had any effect so far. David goes to talk to one of the few who can still talk, asking him where he was, but it's useless, the patient is delirious. Only the Guards are affected, and only they know where they were when they came down with it, because they were on maneuvers. David asks the doctor when the unit was in Iraq, and the doctor says they weren't. He says the symptoms have included delusions, as well as headaches, flu-like symptoms, blurred vision, muscle pains. He said it all happened pretty quickly - from perfect health to coma state took only five days.
At the lab, Carlos checked the fish and found no obvious abnormalities. Bob has found chromosomal abnormalities in the children, and Jill has found something in the bacterial counts called radiodurins. This bacteria can fix itself even after being blasted with radioactivity, and if found in large quantities can indicate the presence of radiation, which is known to cause genetic abnormalities. Jill suggests they test the fish for radioactivity, so Bob and Mayko do that, discovering that the mussels from off the coast of Port Big Horn register radioactivity. Using those as a baseline, they determine where the levels of radioactivity are the highest, and plot them on the map. They find the levels are highest approaching the islands of St. Pierre and Miquelon (which are part of France), where there are oil wells, which causes NORM - Naturally Occuring Radioactive Material - but the levels are too high for that. Bob says they have to look for something that might have been dumped there, possibly by the Russians or the Americans, or the French.
David calls Carlos to find out what they've been able to find out regarding the soldiers. The bloodwork showed some sort of infection, but it's not bacterial, so they think it might be a retrovirus. Jill tells David of Bob and Mayko's work, but David is skeptical that there would be enough radiation in the fish to cause genetic damage.
Back at his apartment, Toumas is waiting for David. He was looking for matches, but he found a letter that David had written to his father when he was a child, saying that he was going to take his mother away so that Toumas could never hurt them again. Toumas wants to know what he did, but David tells him that it doesn't matter anymore. David sits on the couch beside his father, and tells him he's glad he's there. Toumas tells David again that he has Alzheimer's, and that he doesn't want it. He doesn't want to fade away to someone no one recognises.
David is in his office, contemplating the symptoms of the soldiers, when Caroline walks in. He tells her that everyone says there is no such disease, but he swears he's seen it before. David says he's working on it, but Caroline wants to know what everyone else is doing. Bob comes in with an update, but Caroline wants to know right now. David tells her briefly about the GMO fish, and she says they have to put it on the back burner. David tells her that they should tell Bob and Mayko this together. Once they present all their findings to her, though, Caroline says she'll make some phone calls and get the French to clean up the radioactive waste. Mayko says it won't be that easy, as there was a territorial dispute over the islands, and Canada owns the territorial waters where the French nuclear rods were dumped. She says she'll take care of it and leaves. David then tells Bob and Mayko he doesn't think the radioactivity is the cause of what's wrong with the children because there aren't enough other people affected. "Symptoms don't lie," he says, then something dawns on him and he goes racing from the room. He goes to Jill and describes just the symptoms of the soldiers, and she says its encephalitis lethargica, which is highly contagious but was eradicated in 1928, so there is no vaccine. They both look appalled as they contemplate the possible consequences of a virus like that in the hands of a terrorist group.