The race for the first atomic bomb heats up, and we learn more about the human cost in terms of safety and security protocols on this week's episode of Manh(a)ttan. "Acceptable Limits" proved to be another more leisurely paced episode, yet tightly plotted, methodically moving pieces in place for what promises to be some fireworks next week.

We see a man walking through a town that is not Los Alamos -- it has a European vibe -- into a university building and then a room that looks a lot like Ackley's and Winter's labs: scientists scribbling on blackboards and drinking cup after cup of coffee. When a second man marches through the corridor with an air of authority, the others greet him: "Good morning, Dr. Heisenberg." This is the headquarters of the German Manhattan Project, America's foremost competition in the race to build an atomic bomb, with the outcome of the war at stake.

Back in the New Mexico desert, Frank Winter is definitely feeling the pressure, trying in vain to get useful information about various fissile material tests out of his lovestruck junior scientist, Fritz, who is vague on firm data on certain key properties. He can't help talking incessantly about his lady love, Jeannie -- the working girl who reads Dickens and charges him for their highly chaste (so far) "dates." (When his co-workers tease him about this, Fritz points out that "all girls cost money" in terms of dinner, drinks, and the movies; at least with Jeannie it's a flat rate.)

We learn the clock is ticking because an X10 nuclear reactor is about to go online at another top-secret site in Tennessee -- the future Oak Ridge National Laboratory -- and Frank's group needs to demonstrate their competence with the precious bit of Pu-239 they've been given, in hopes of being given more. The prior samples came from Enrico Fermi's lab in Chicago, made in teensy amounts in a cyclotron, which is why the substance is so precious; the X10 reactor will scale up production of Pu-239 from micrograms to kilograms.

"We're about to have our very own plutonium factory," Ackley tells Charlie after the latter gets yet another full physical prior to a top-secret business trip to that very site. Ackley is concerned that the military, in its rush to beat Germany to a bomb, isn't quite as concerned with safety as they should be, given the potential destructive power of a nuclear critical reaction should anything go wrong. Charlie is being sent to do a safety review.

And he's not going alone: Helen Prins, the sexually liberated sole female scientist in Winter's group, is traveling undercover with him as his "wife." Given that things are still tense between Charlie and his actual wife, Abby, after last week's plagiarism accusations, this is probably not going to help matters, especially since Charlie neglected to share this fact with Abby. She learned it about from Liza Winter, who let it slip in casual conversation.

Interesting tidbit, courtesy of UCLA physicist David Saltzberg, who consulted on this episode: while Helen is an entirely fictional character, there was a young female physicist who worked with Enrico Fermi on the first nuclear reactor, later supervising the construction and operation of the nuclear reactor at Hanford in Washington State: Leona Woods Marshall Libby. She later recalled the oppressive mood among the scientists in those days in the race to be first with a nuclear bomb:

"I think everyone was terrified that we were wrong [in our way of developing the bomb] and the Germans were ahead of us. That was a persistent and ever-present fear, fed, of course, by the fact that our leaders knew those people in Germany. They went to school with them. Our leaders were terrified, and that terror fed to us. If the Germans got it before we did, I don't know what would have happened to the world. Something different. Germany led in the field of physics. In every respect, at the time war set in, when Hitler lowered the boom. It was a very frightening time."

Things have smoothed over between Frank and his closeted gay mentor, Babbit -- he is once again having a friendly dinner chez Winter. Liza regales Babbit with the tale of Frank's gift to her on their second wedding anniversary: a rabbit in a box. Frank decided the rabbit was an appropriate symbol of their marriage: something about shared curiosity and "a keen mating instinct." But within a week the rabbit developed sores all over its body and started banging its head against the cage, and died soon after. Turns out Frank stole the rabbit from a biology lab, where it was part of an infectious disease study. "Awww, you gave your wife syphilis. That's nice," Babbit teases. It's tough not to see the rabbit story as ominous foreshadowing, given the current stresses on the Winters' marriage.

Fritz is working long hours conducting experiments with the Pu-239 to get Frank the hard data he's demanded. Alas, there is an unexpected chemical reaction. Fritz later calls it a rapid vapor expansion -- a sudden pop and puff of smoke, right in his face. Paul Crosley and Jim Meeks (Christopher Denham) return to the lab to find Fritz in his underwear, on the floor with Geiger counter and scope, desperately searching for the missing plutonium. Crosley is incredulous: "You've misplaced a million dollars of Pu-239?" Misplaced isn't quite the right word: Fritz inhaled the full 24 micrograms of this radioactive substance. Crosley and Meeks rush him to the medic, where Dr. Edelman (Adam Godley) pumps his stomach and presents poor Fritz with the contents, telling him he'll need to recover the plutonium from all that "organic matter."

To Frank's credit, his immediate concern is with Fritz's health, and he is appalled at Edelman's "prescription": aspirin and a case of beer, with instructions to collect all the ensuing urine. "But how do you feel?" Frank insists. "A little buzzed from the beer," Fritz admits sheepishly. Fritz, Crosley and Meeks are a bit too blase about the odd effects of ingesting even a little Pu-239. They work their way through the case of beer and end up drunkenly making wagers on just how far away the Geiger counter can detect the radiation when Fritz strongly exhales.

Today we know all about the dangers of ionizing radiation, which includes x-rays, as well as the alpha, beta and gamma radiation emitted as plutonium decays. An ion’s electrical charge can lead to unnatural chemical reactions inside biological cells. It can break DNA chains, causing the cell to either die or develop a mutation and become cancerous, which can then spread. Fritz inhaled a tiny amount, but it's easier for plutonium to cross into the bloodstream when it is inhaled, and from there it accumulates in the bone marrow, the liver and other major organs. And it has a biological half-life of 200 years, exposing the surrounding tissue to even more radiation. (That said, several Los Alamos workers inhaled a good amount of plutonium dust in the 1940s, with no corresponding spike in incidents of lung cancer. So maybe Fritz will be okay.)

Frank confronts Edelman, who assures him the scientist's exposure was within "acceptable limits." Edelman "followed the Q9 directive to the letter," but when Frank asks who wrote that directive, all he gets is "That's classified." Edelman's ignorance of radiation and its effects on the body is soon unmasked; he's an obstetrician by training. Frank demands that the project medical director be summoned to examine Fritz, but thanks to compartmentalization, Edelman has no idea who that might be.

Thus begins an elaborate cat-and-mouse dance as Frank attempts to chase down exactly who has been getting the blood and urine samples routinely taken from workers in the camp. Edelman's assistant just drops them off to be posted, and they are supposedly analyzed elsewhere by the "project radiation chief." Eventually Frank gets through to a ranking doctor and asks to speak to this mysterious project radiation chief. All the doctor knows is his security ID number, B-379, and calls the assigned extension. Edelman's phone promptly rings, to the doctor's shock. It's all an elaborate illusion -- security theater. Apparently nobody has been analyzing all those blood and urine samples; everyone just assumed someone else was handling it.

Charlie isn't thrilled about traveling with Helen, perhaps remembering how she played him a few episodes back to get hold of some plutonium. At the airport, he complains about Helen's extra luggage: "How many pairs of shoes do you need?" She fires back with a dig about finding a grammatical error in "your little space paper" (Charlie confused "affect" and "effect"), and spins a tall tale for the woman at the ticket counter about how she supports her poor deadbeat husband -- just for a little added humiliation. They are so filing for fake divorce when they get back to Los Alamos.

Still bickering, "Mr. and Mrs. Donaldson" arrive at the reactor facility in Tennessee and are met by the man in charge, one Daniel Ellis (John Carroll Lynch), who is quickly established as a stereotypical Southern good ol' boy, referring to female employees as "pretty little patriots" and brusquely dismissing any contributions from Helen and his black assistant, Theodore Sinclair (Casey Allen), who he would clearly prefer to be seen and not heard.

He shows them the new reactor, a behemoth made of 600 pound of graphite: "She's dressed and ready for her cotillion," he boasts. By tomorrow morning, "She'll start spinning uranium straw into plutonium gold." (Helen notes his choice of pronoun approvingly and declares, "All reactors should be female.") There were actually two fissile materials used in the bomb effort: uranium-235 and Pu-239. Most uranium is actually of the stable (non-fissile) U-238 variety; U-235 is an isotope, meaning the nucleus has the same number of protons but three fewer neutrons. Because the two are so chemically similar, it's very difficult and expensive to separate them chemically. It's much easier to separate Pu-239 from U-238, because they are different elements.

Anyway, Ellis' friendly demeanor soon turns hostile when Charlie starts asking too many questions about safety procedures. Theodore helpfully suggests that Charlie would find the facility's schematics more informative than a lengthy tour, but Ellis cuts him off and sends him for coffee -- BURN! -- telling Charlie that he is here to grease the wheels, not gum up the works. "I'm here to make sure you don't set the atmosphere on fire," Charlie retorts. Then he pulls rank and plays the Oppenheimer card, since Oppie's orders outrank Ellis' deadline.

Up until now, Helen has been mostly playing along with Ellis, but she follows Sinclair on his coffee run. "When I get dismissed by a group of men, usually it means they're afraid of what I'm about to say," she offers. Sinclair is initially defensive and rejects the olive branch: "This isn't the underground railroad. I don't need a woman to rescue me from the white man." Undeterred, Helen points out that "no one else in that room gives a shit what you think," but she does. He pauses for a beat and then says, "Green water," before stalking off.

"Green water," as we learn in the next scene, is what happens when uranium dissolves into liquid form. The neutrons slow down and become 100 times more fissionable. That's why safety protocol demands that no more than 12 kilograms can be stored in any given building; nobody wants a nuclear chain reaction to begin spontaneously. When Helen and Charlie review the blueprints, she notices that the renderings are off in scale by a good six inches. The uranium storage units are too close to each other. Helen tells Ellis he'll need to clear all those vats, spread out over 100 acres, a process that will cause a week's delay. Charlie backs her up: "You heard my 'wife.'" Finally, they're working as a team.

Meanwhile, Frank is hot on the trail of just who who hired Edelman, knowing he'd probably just follow the directive and not ask too many questions. That would be Alex Barath (Johnny Coyle), a fellow scientist, who we've seen briefly in prior episodes. Frank confronts Barath about why he hand-picked an inexperienced obstetrician as the camp's ranking medical officer. Why not give the position to Barath himself? The Hungarian-born physicist worked with Marie Curie as a young man at the Pasteur Institute, and hence had firsthand experience with radiology.

Curie famously died of leukemia at age 67, very likely due to her years of exposure to ionizing radiation in the lab. Frank is correct that her lab books turned out to be highly radioactive -- so much so that when scientists placed photographic plates between the pages, the resulting films revealed her fingerprints, made from radioactive deposits wherever she touched the paper. She publicly never spoke of the risks of radiation exposure, but Frank reminds Alex that she never let him handle the radioactive materials in the lab, either -- likely to protect the young man who, he implies, had fallen in love with her.

His worst fears confirmed, Frank resolves to confront the issue head-on at the upcoming town council meeting: "People need to know you're running a Potemkin clinic and it's all a lie." Barath warns him not to shout "plutonium!" in a crowded theater; Frank won't just lose his job for this, he could well end up in a military prison.

Meanwhile, Liza is investigating who or what killed her beloved honeybees in preparation for the same town council meeting, where she plans to make a stink about -- among other things -- the Army's use of the toxic pesticide DDT all over the base. Apparently studies with mosquitoes ended up with the exposed insects having violent seizures and bleeding internally until all their organs failed. Liza could really use a microscope to aid in her investigations, but when she asked Frank and Babbit to "borrow" one for her from the lab, they refused -- the Army is very strict on that score and monitors equipment too closely. She ends up borrowing one from the schoolhouse.

In the end, neither Frank nor Liza testify at the town council meeting. He is dissuaded by Colonel Cox, who shares top-secret information with him provided by a German spy (going by the code name "Magpie") indicating that the German bomb effort is two months ahead of the Los Alamos project. When Frank sees the accompanying equations, he realizes the Germans are already testing yields -- they are more than two months ahead. If Frank raises a stink about the medical charade now, it will result in a weeks-long delay, giving the Germans even more of a head start. And if the Germans drop a nuclear bomb, "none of this makes any difference," Cox warns.

By now Frank has amply demonstrated his single-minded prioritizing of the bomb development over everything else, so his decision is never in doubt. He takes Cox's advice and remains silent. Chalk it up to just another human cost of wartime science. At least it's within the "acceptable limits," right?

However, he does make one change to keep his people safer. Following Marie Curie's lead, he insists that from now on, only he will be handle the radioactive plutonium in the lab -- although he makes them think it's because he doesn't trust them, thanks to Fritz's stupid mistake. God forbid he should show an inkling of warmth or humanity to his team.

Or to his wife. He returns home to find her still working on the case of the dead honeybees, having skipped the town meeting for lack of evidence. She didn't find any trace of DDT or toxic pesticides in her dead honeybees, and she also ruled out infectious diseases, so it's not due to a virus or parasite. "You'll figure it out, you always do," Frank says in consolation -- but he changes his tune quickly when she asks if there might be something toxic in the tech area that's at fault. This is hitting a bit too close to the truth, so naturally he lies to her -- what's one more lie when he's told so many by now? -- and claims he personally read all the environmental safety reports.

When that doesn't work on the tenacious Liza ("A bee colony doesn't just collapse on its own!"), he tries the old-school, "it's all in your head, dear" line. Liza is insulted and hurt by the ploy, as she should be, especially when Frank follows up with a patronizing "We'll get you some new bees." She rebuffs him when he tries to stroke her face. And does she give up? Hah! We last see her pulling the preserved purple chrysanthemum she'd picked way back in the pilot from the pages of a book. Liza always figures things out.

Meanwhile, back in Tennessee, Helen and Charlie arrive on-site to find the staff have already begun unloading the various rods, as Ellis smugly informs them that the reactor should be fully operational within a day. It's been given a clean bill of health on the storage by the military. Charlie points out they'd made a list of 22 major hazards to resolve -- it wasn't just the storage issue -- and Ellis assures him the Army will "give your list the consideration it deserves -- just as soon as we're critical." And he tells Charlie it's no good playing the Oppenheimer card again, since the current directive comes straight from General Leslie Groves' authority: "the guy who hired Oppenheimer." Once again, safety is sacrificed for the greater good.

Will the fate of Liza's bees be tied to the radioactive substances being handled in the tech sectors? Will Fritz still be breathing radioactivity (and might Jeannie finally relieve him of his virginity)? And surely we'll see what happens when the Oak Ridge reactor comes online, and whether Charlie and Helen are right to be concerned. (Hint: they probably are, because History.) We'll also have more commentary from David Saltzberg on the underlying physics of next week's episode. So stay tuned!