Relationships are fraying right and left, with betrayal, after betrayal after betrayal, this week on Manh(a)ttan, as we kick off the first ("Tangier") of the final three episodes of the season.

You might remember that Colonel Cox told Frank Winter about a German scientist dubbed "Magpie," who was passing secrets to the US on the Nazi progress on their own bomb development program. We haven't heard anything further about that, but this week we get to meet the Magpie himself (Marc Comstock) -- all too briefly, since he is strong-armed by SS officers into a back room, where they are holding his wife with a gun to her head. He is given a choice: if he admits to spying for the US, they will spare his wife. A terrified, tearful Magpie admits it is true, upon which his wife is summarily shot. The officer tells him he has spared his wife the shame of living with a traitor, and instructs his officers to cut off Magpie's head and send it to Washington, DC. (He is mercifully shot first.)

It's a hell of an opening scene, and the shock waves reverberate through the rest of the episode. Colonel Cox arrives at his office to find the sinister Occam waiting for him. Occam is not happy, and when Occam is not happy, bad things tend to happen. He wants to install hidden microphones all through Cox's office, monitoring every last bit of gossip among even the secretaries. When Cox objects, Occam says it's on General Leslie Groves' orders, after the general received Magpie's head in a box. "Magpie's dead and now we have no eyes on Heisenberg because somebody talked," Occam says. Cox denies anyone on his staff leaked the information, but hesitates just long enough for Occam to become suspicious, asking who else outside the office Cox might have told.

It was Frank Winter, of course -- already on Occam's hit list, for reasons that remain a bit murky. During a barbed exchange with his rival Ackley, Frank learns that his mentor, Babbit, has quit the implosion team and taken an administrative position in Oppenheimer's office. When Frank confronts Babbit, insisting he can't succeed on implosion without him, Babbit tersely responds, "You're gonna have to." And he rebuffs Frank's attempt to get him to report back on anything said about implosion, clearly weary of all the lying and scheming and petty politics, not to mention the high human cost.

Frank is definitely playing a dangerous game, and if he has any doubts about the stakes, those are no doubt erased when he arrives home to find Occam waiting for him, accusing Frank of having gotten Magpie killed by leaking the news that the US had a spy on Heisenberg's project. "You think I sold him out to Hermann Goehring?" Frank asks incredulously. "I think it's far more complicated than that, because you are far more complicated," Occam replies. Frank suggests that since Occam likes complexity so much, "why don't you try quantum electrodynamics?" Occam says the only math he's ever been good at is "eliminating variables," and proceeds to demonstrate just how much he knows about Frank and his people, marveling at the loyalty demonstrated by suspected communist Glen Babbit, the late Sid Liao, and even Jim Meeks, who looks like he'd fold at the first hint of tough questioning but still remains loyal to Frank.

Occam finds this strange, since his only loyalty (he claims) is to his country. "You collect people, dented people with little cracks in their Bakelite, where the funniest impurities seep in," Occam concludes. "The only question is which of these broken men did you trust with Magpie's identity" -- or maybe, he adds, he told his wife, or his maid, Paloma, implying that he knows full well about Frank's affair with the latter. I'm hardly a fan of the spooky interrogator, but Occam has a point: Frank did tell others about Magpie, namely Charlie -- and who knows who Charlie may have told (although he later denies having done so)? Someone betrayed the doomed Magpie, and one can hardly blame Occam for wanting to find out who, especially since we've known since the pilot that there is a rat somewhere on the project.

We don't see much of Liza this episode, but she's having a rough time of it after last week's breakdown, having given up working and dutifully taking her prescribed phenobarbitol to ward off anxiety and hysteria. Her last remaining pleasure is a spot of reading under one of the rare cottonwood trees in the civilian section on base.

But it seems even that will be taken away: she confronts a group of soldiers in the process of tearing down her favorite tree, on orders of the Civilian Town Council, whose members are pretty much puppets of the military. They vote how they're told to vote, and in this case they've voted to clear the cottonwood trees to make room for extra housing, since several thousand new scientists are arriving in a few months, "and they all want formica counter tops," a solder tells her, adding (with a hint of sympathy), "You'll never beat the army, lady. Maybe pick on someone your own size."

On the romance front, we find Paul Crosley and Helen Prins in the desert on the morning after an overnight camping trip -- because Crosley wanted "love under the stars." Only Helen isn't in love, rejecting the slightest hint of a love token when he tries to place a flower in her hair. He is equally excited about the progress they've been making on the implosion design, breaking compartmentalization to tell her they've cracked the shock wave problem. Helen, of course, knows all about it but pretends otherwise, telling him that while the breakthrough is a great start, it still doesn't "put implosion in the catbird seat" -- and Crosley in turn teases her about her use of the American slang.

Undeterred by his lady love's aloofness, Crosley insists they go on a double date with Fritz and his paramour-for-hire, Jeannie (she charges by the quarter hour, which makes her relationship with Fritz pretty profitable). He mostly sulks the whole time, though, because he's biding his time to make a Grand Gesture in the form of a declaration of love and marriage proposal to Helen. I think it's safe to say Helen didn't see this coming. Crosley gives quite a touching speech about how much he respects and admires her, and doesn't want to own her, or limit her freedom. Helen visibly softens as he talks, and for a moment one might think she'll consider the proposal seriously.

But when Crosley comes to her room later that night, hoping for an answer, she sadly tells him that's just not who she is, and maybe they shouldn't see each other anymore. Hurt and bewildered, he flings the door wider and sees Charlie standing in her room. "It's just work," Helen assures him -- truthfully -- but he's having none of it and storms off, to her chagrin. "Don't you say a word. He's a good man," she tells Charlie fiercely, who shrugs it off.

Ackley, too, has noticed Charlie spending time with Helen, and is also convinced they are having an affair. About to leave on a short trip, he stops by to tell Charlie that he knows what's he's been up to. Charlie initially fears the worst, thinking Ackley has figured out he's got his team fooled into working on Frank's implosion project, and is visibly relieved when Ackley launches into a mini-sermon on how "family is everything," ordering him to end his "entanglement" with Helen. When Helen comes into his office with Frank's latest assignment, he tells her they need to stage a breakup. She takes perhaps a bit too much relish in slapping him in front of his colleagues, including the perpetually leering Tom Lancefield, who groped Abby a couple of weeks ago.

Speaking of Lancefield, he goads Charlie into joining the boys for Texas Hold 'Em poker that night, even though Charlie initially insists he doesn't gamble. He changes his mind, ignoring taunts from Lancefield about whether his "pretty little wife" would approve. And naturally the two end up facing off in heads-up action across a very big pot. First, Tom (who hails from a wealthy family) makes a huge raise pre-flop -- the equivalent of half a year's salary, apparently -- which Charlie calls by signing over his paycheck and putting it in the pot (since he does not hail from a wealthy family). The flop is so-so: 9 of Clubs, Queen of Spades, and 7 of Hearts. Charlie and Tom both check. The turn is the 5 of Hearts. They both check again.

The final card is the King of Clubs. It's not the most auspicious set of cards -- unless one of them happens to be holding Jack-10, or pocket Kings or Queens -- but a cocky Lancefield raises big, telling Charlie he knows how badly he wants to beat him. Is he bluffing? Maybe. Charlie certainly thinks so, offering a rough schematic of his as-yet-unpatented design for a microwave oven, claiming to have cracked microwave transmission while working on radar as a grad student. (It's artistic license. Percy Spencer, a scientist with Raytheon during the 1930s and 1940s, is usually credited with the invention of the microwave.) "Take the pot, it's yours to patent," Charlie says. Since this amounts to a value of around $8000, it proves too rich even for Lancefield's blood, and he folds what turns out to be Ace-8 (unsuited). So he was bluffing; at best he had high card. But Charlie was bluffing, too, with a measly 2-3 (unsuited). Go, Charlie! If this physics thing doesn't work out, he's got a fine future as a card shark.

Or a maybe a pugilist. As he collects his winnings, Charlie informs Lanefield that he has a tell: a wink in his left eye whenever he doesn't get what he wants. "Here, let me show you." And he summarily punches him in the face, and tells him if he so much as looks at Abby again -- never mind grope her -- he will break his neck. It's what he should have done two episodes ago, and the fact that he didn't tells Lancefield he's got something to hide. "You're pulling one over on Ackley," he taunts, making it clear he knows their calculations are for implosion, not Thin Man -- and as soon as Ackley returns from his trip, he'll blow the whistle on the scheme.

Frank is not happy when Charlie tells him about the threat, and since they can't bring Lancefield into their fold, he suggests Charlie plant some confidential files in his home or office to get his security clearance revoked. The powers that be are far more likely to believe Charlie than "a disgruntled former employee." Yes, it's the Winter Dick Move of the Week; he's amassed quite a few of them by now. Frank assures him Tom will just be shipped back to Chicago -- to which I have to interject, COME ON! They shot Sid Liao dead for having classified files outside the office! It's not clear what would happen to someone violating the policy of compartmentalization, but it probably wouldn't be a slap on the wrist, even for the well-connected Tom Lancefield. But Frank insists "We're playing a zero sum game. Every move costs a piece. And this piece tried to rape your wife."

Charlie caves to the pressure, convincing himself that Lancefield will land on his feet in the end. And he decides to exploit Abby's friendship with Elodie, asking her to plant some files in a crawl space under the kitchen (the floor plan is identical for all their houses). He has no idea of the nature of Abby's relationship with Elodie, of course. She has just spent a delightful afternoon with her lover, playing a game of Elodie's design called "Escape."

"For $100, where should we go?" Elodie asks, poring over a world map. She is mock-disappointed at Abby's lack of imagination when she suggests Albuquerque, but is suddenly more somber when Abby says (in essence), hey, you're French, how about Paris? "Paris was real for me, before the war," Elodie says -- not a fantasy. "I do not think there will be much Paris left." Then she lights upon the city of Tangier -- from whence this episode gets its title -- a free city filled with artisans, lovers, writers and renegades, completely untouched by the war, and hence just the ticket to fuel their playful fantasy.

Anyway, Abby is justly horrified at Charlie's suggestion that she help him frame Tom Lancefield to get him fired, especially at his insistence that wars have casualties. "I don't even even know who I'm talking to," she declares, before walking out. She goes straight to Elodie and asks if they can run off to Tangier together for real; she has money stashed away that Charlie doesn't know about. When Elodie asks what happened with Charlie, she lists a string of grievances, ending with him asking her "to do things no one ever should. I don't know who Charlie is anymore. And I'm not sure he ever knew who I am." After a spot of lovemaking, a partially disrobed Abby goes into the kitchen to get Elodie a glass of wine -- and spots the panel in the kitchen floor, just as Charlie described.

Cut to daybreak, as a subdued Abby returns home and finds a repentant Charlie awake and waiting for her. Charlie starts to apologize for dragging her into the mess, admitting he should have followed his own conscience rather than ask her to betray her friend. He stops mid-sentence because there is a commotion outside, and he realizes, shocked, that Abby has done what he asked. Tom Lancefield and Elodie are being dragged out of their home into waiting cars by MPs. The anguished look Elodie gives Abby makes it clear she realizes what her "friend" has done and it has cut her to the core. It was a monstrous act, and Abby's body language shows she knows it.

Honestly, I had to re-watch the final 10 minutes to clear up my confusion about Abby's sudden shift in priorities, because the twist seemed to come out of nowhere. Rachel Brosnahan's performance was so subtly nuanced, if you weren't watching closely it was easy to miss. And perhaps I'm reading too much into it. But when she walks into the kitchen to get Elodie that glass of wine, all smiles in the afterglow of their lovemaking, she glances out the window and spots a young family -- husband, wife, and two small children -- walking happily hand in hand down the street. And that smile slowly fades. That's when she glances over to the panel to the crawl space under the kitchen floor.

We haven't seen much of Abby's toddler in recent episodes; she's been flushed with the excitement of her love affair and preoccupied with the tension between her and Charlie, relying on a nanny to watch over her son. But that glimpse of domestic happiness seems to snap her back to reality, making her realize that sure, you can dream of an escape to Tangier, where there aren't any secrets or obligations or cumbersome responsibilities, and no ugly world war.

In the end, though, it's just a dream, however much Abby wanted to make it her reality and shed her role of dutiful traditional wife and mother -- at least for a moment. By betraying Elodie so ruthlessly, she's shed her delusions and chosen her future with Charlie, for better or for worse. Not that it sits well with her: the final shot is a grief-stricken Abby retreating to their bedroom and locking the door, Charlie plaintively knocking and asking her to let him in.

And in the end, Abby's sacrifice was all for naught, because while Frank and Charlie were focusing so narrowly on the threat posed by Tom Lancefield, they neglected to spot the viper in their midst: the spurned and heartbroken Paul Crosley, who's already wobbled once on the loyalty front. Crosley has opted to throw himself into his work to soothe his aching heart, and stops by Frank's office to express how proud he is of the progress the team has made in recent weeks. Frank nods distractedly and says that while using baritol is a start to solving the speed problem (remember they need to vary the burn rates of the point explosives to turn the shock waves inside out), "it doesn't put implosion in the cat bird seat."

Crosley recognizes the same slang Helen used on their camping trip, and the truth slowly dawns on him, seeping through the cracks in his Bakelite, as Occam might say. Hurt at being shut out, he finds the calculations from Ackley's team in Frank's office, and marches over to Ackley's home. At the first mention of their work on implosion, Ackley reminds him, "Implosion is Frank Winter's country. The border's closed." Crosley pulls out the papers with a flourish and hands them to Ackley: "I believe your border is wide open." Hell hath no fury like an Englishman scorned.

We'll soon to find out which relationships will survive, and just what the consequences might be for violating compartmentalization as this intricate web of secrets and lies that's been building up over the entire season starts to unravel, big-time. I'm guessing it won't be a slap on the wrist.