Secrets have a way of coming out, one way or the other, despite one's best efforts to contain them, and boy howdy, do they ever on the penultimate episode of Manh(a)ttan. In the process, "The Gun Model" finally sheds some light on the enigmatic cipher that is Reed Ackley, head of the Thin Man design team.

Last week Ackley learned about Frank Winter and Charlie Isaac's unholy alliance to siphon resources from the Thin Man group to solve the implosion problem. What will he do with this information? We find him sitting alone late at night in his darkened office, rifling through requisition forms, all signed by Charlie, when an MP barges in, surprised to find the division head still on the premises.

"Boldly they rode and well/Into the jaws of death/Into the mouth of hell," Ackley intones -- you know, just to set the mood. He's quoting Tennyson's "The Charge of the Light Brigade," written to honor the fallen soldiers in the Battle of Balaclava during the Crimean War. One line Ackley didn't quote: "Not tho' the soldier knew/Someone had blunder'd" -- and that blunder cost the brave soldiers in the brigade their lives. There have been plenty of blunders this season on Manh(a)ttan, and now we're finding out just what the cost will be for our characters.

Abby has not forgiven Charlie for pressuring her into framing Tom Lansfield, betraying Elodie in the process, which is why Charlie is sleeping on the living room couch when Ackley knocks on his door in the wee hours, a rifle slung over his shoulder, and invites him to go hunting in the desert. Once there, it's clear Ackley isn't interested in hunting wild pigs. He wants to know why Charlie shot him in the back by trying to sabotage Thin Man via his collusion with Frank Winter. At least he's being direct. So Charlie comes clean about the issues with Thin Man: namely, the spontaneous fission rate for the plutonium being manufactured at Site X (the future Oak Ridge National Lab) is too high and the bomb will pre-detonate.

David Harbour as Reed Ackley and Ashley Zukerman as Charlie Isaacs.

Ackley insists the actual bomb will be using weapons-grade plutonium made at the nascent "Site W" -- his trip was to Washington state to tour the new Hanford plant, and Ackley claims that the plutonium made there is as pure as the stuff made in Enrico Fermi's cyclotron in Chicago: "I have the fission rates on my desk." If you're wondering why this should make any difference... well, you should be wondering. Ackley's answer is that it's better because it was designed by Fermi himself. I am disappointed in Charlie for accepting this as an explanation on its face.

Ackley tells Charlie he's been manipulated by Frank, who (Ackley claims) cares more about cementing his place in history as the architect of an implosion bomb than the outcome of the war. It's true, the whole scheme was Frank's idea, and Frank has shown himself willing to sacrifice just about anyone to make implosion work, right down to insisting Charlie frame Tom Lansfield. Since Charlie signed all the requisition forms, it will be Charlie who pays the price should the military find out about this huge violation of compartmentalization. But then, surprisingly, Ackley promises to protect Charlie, if the latter will trust him.

Why isn't Ackley furious with Charlie for the betrayal? We get a hint during a top-secret meeting of military brass and high-clearance scientists, announcing that the larger sample of plutonium is now ready for transport from Site X. Ackley insists on tighter security measures: a heavily armed military convoy, even though this will delay delivery of the plutonium by several weeks. He mentions a betrayal by one of his own scientists -- but names Lansfield rather than Charlie, despite knowing full well it was a frame-up. When Babbit (now working in Oppenheimer's administrative office) ingeniously finds a way to fast-track a convoy within a few days instead of weeks, Ackley claims this might still be insufficient. Ackley is trying to delay delivery of the plutonium. But why?

He also confronts Helen Prins, trying to undermine her loyalty to Frank with a story about his own history of sticking up for Frank when the older physicist inevitably pissed off the wrong people, only to find himself twisting in the wind with Frank nowhere to be found: "It taught me a valuable lesson about politics. And about Frank. Great men are not always good men." When Ackley asks if she was involved in the scheme -- Charlie refused to implicate her -- she claims she was coerced. He offers to protect her, too, in exchange for her trust. Helen goes running right to Frank with the news that Ackley is onto them, and is moving the proverbial chess pieces around the board to ensure Frank takes the fall for the whole mess.

So playtime is over. The clock has run out. They need that plutonium from Site X as soon as possible to prove that the gun model won't work and implosion will. But Frank can't do anything about it himself because his security clearance has been mysteriously downgraded. Colonel Cox won't help either, even when Frank insists Thin Man will pre-detonate. Cox points out that the only way he could know that is if he violated compartmentalization in some way, thereby incurring severe consequences. Does he really want to make that declaration official? Frank wisely backs down.

Meanwhile, if Paul Crosley was hoping for a reward by ratting out Frank and Charlie to Ackley, that plan backfired. Nobody likes a snitch, even one with a posh British accent -- especially if said snitch comes bearing an inconvenient truth. Since he can't work with Frank anymore, and Ackley thinks he's disloyal, Crosley asks Babbit to transfer him to Site X. "Whoever we once worked for, Frank has become someone else," he declares, having guessed that Babbit, too, had been left in the dark about Frank's scheme. Babbit says he'll see what he can do.

Liza Winter has decided to run for the Town Council. Her competition includes a nervous man who spends his entire campaign speech claiming he wasn't a peeping Tom, nosiree, he was birdwatching, and for his opponent to suggest otherwise is shameful. Ah, local politics. When it's Liza's turn, she comes clean about her mental troubles because "I don't believe in keeping secrets anymore." She demands that Colonel Cox explain precisely what rights she and the other civilians on base have, and what recourse is available if they feel those rights are being violated. "The war for American values is being waged right here on this Hill. I believe transparency is the lifeblood of democracy," she concludes. "I'm asking for your vote." You go, girl!

We find Abby is brooding in the kitchen of the now-empty home where she and Elodie spent so many blissful hours together. She finds a playing card on the floor, part of Elodie's deck with the rather risque artwork (a female nude). She is interrupted by a cheerful young woman named Evelyn, newly arrived from Berkeley with her husband, a scientist joining the Manhattan Project -- they have been assigned the Lansfields' former quarters. Evelyn is quite a bit like Abby was when she first arrived on base. Maybe that's why Abby slaps her and snaps, "Wake up!" before stomping out. Abby has lost her innocence; I kind of like her new edge.

She is equally frosty when Frank shows up at the door to see Charlie and try to win him back over to Team Winter, insisting that it is Ackley (not him) who can't be trusted. He scoffs at the notion that the Site W plutonium will be any purer: "I guess Reed Ackley figured out a way to rewrite the laws of physics." Frank wants Charlie to use his security clearance to get the plutonium delivered from Site X right away. Charlie refuses and the two trade verbal punches, with Frank taunting Charlie with how vulnerable he is because his name is on all those requisition forms. Charlie retorts that Frank has compromised every person on his team and driven his wife mad by dragging her out to the desert, all for the sake of his implosion baby, declaring, "I am not going to be the last casualty of Frank Winter's ego." So there.

After Frank leaves, Charlie tells Abby he trusted the wrong man and betrayed his mentor, but that Ackley was giving him a second chance with a clean slate. Her response is a withering, "There's no such thing as a clean slate. For any of us." From her perspective, there's no difference between Winter and Ackley. They are opposing sides in an intricate political chess match and Charlie is just a pawn in their machinations. She wants to leave the Hill and go home to her family, and when Charlie reminds her the Army would never allow that, she says the Army will under one condition -- if she and Charlie divorce.

Just when it looks like Frank has run out of options, we find that Babbit has had a change of heart following his conversation with Crosley. Fritz accompanies Babbit to the base entrance, where none other than our good friend Dr. Sinclair -- the sole black physicist at Site X -- is there with an early delivery of the plutonium, lured there with the promise of a permanent position on the Hill. Maybe he can have Babbit's job, since the latter will likely be fired for abusing his position in Oppenheimer's office to get the plutonium, torpedoing his career. (Seriously, why does Frank inspire such loyalty?)

Thus far on the series, Ackley has been a pretty cool customer, but we see his uber-confident mask start to slip in a touching scene with his wife, Rose (who seems to know all about the Gadget, which surely must be a breach of security) helping him with his tie: "Men like you shouldn't be thinking about apparel," she says, convinced her husband is going to win the war for America. He says they might not need Gadget to beat the Germans after all, and suggests they should just pack up and go home to Chicago for the rest of the war. Rose brushes this off: surely he would be called to Washington by the President, and she's already thinking about the prestigious dinner invitations they'll receive. "I don't know about that," he says with the tightest of smiles, tearing up just a smidge as an assistant bursts in with news of an urgent call from Site X, no doubt with the news that the plutonium has been delivered.

Charlie finds Ackley in the lab feverishly writing equations on the board in a last-ditch attempt to save his Thin Man. He's calculated muzzle velocity and barrel pressure and thinks perhaps they could extend the barrel so the plutonium could reach a higher rate of speed, thus warning off pre-detonation -- except the only aircraft capable of carrying an 8000-pound bomb can't accommodate the longer barrel. When Charlie tries to tender his resignation, Ackley finally cracks, admitting that he can't fix the problems with Thin Man without Charlie's help. That's why he brought him on the team in the first place; his paper on a new approach to nuclear cosmology "changed the way we think about the universe, the way we think about the creation of the elements. You can fix Thin Man."

Charlie realizes with horror that Ackley has known all along that Thin Man would fail and covered it up for months. Remember that scene several episodes ago where we saw Ackley burning an envelope addressed to Oppenheimer? I'm guessing it was a confession to that effect. Shaken to the core, with his marriage and career crumbling around him, Charlie ends up parked outside Helen's place, and they finally consummate the attraction that sparked on Site X.

Frank Winter (John Benjamin Hickey) finally sees Thin Man implode on WGN America's "Manh(a)ttan."

Frank receives a cryptic message to meet out at the armory blast zone. He expects to find Charlie, but it's a desperate Reed Ackley with his trusty shotgun. This is a bad sign for anyone familiar with Chekhov's Gun. (One variant: "One must never place a loaded rifle on the stage if it isn't going to go off. It's wrong to make promises you don't mean to keep.")

Ackley asks for Frank's help on Thin Man. Frank opts for the harsh truth: "Thin Man is dead. You did the best you could, but your bomb won't run on imagination." Instead of gloating, Frank admits he and Ackley both have blood on their hands, and will likely both end up in the brig unless they form a united front and go straight to Oppenheimer with a recommendation to move forward with implosion.

Ackley is incredulous. "You'll work with me?" Frank insists he will work for Ackley if it means winning the war. Besides, in the end someone will have to go Washington, DC, to advise the president on how best to use (or not use) the most powerful weapon in history, "and I think you and I both know I don't belong in a room with the president."

It's a genuine act of grace in a man who has not exactly been a shining example of ethical behavior thus far, but clearly his actions weren't ego driven -- that was Ackley projecting his own issues onto Frank. "What would you have done if you thought implosion might not work?" Ackley asks. Frank shrugs. "Let it go. Six months from now, all anyone will remember is that we built it." He thinks the matter is now resolved, but as he gets into his car, there is a gunshot. The well-dressed, polished physicist with the too-perfect math has committed suicide, crushed by the humiliation of his failure and the cost (in the form of soldiers' lives) of his own blunder in covering it up for so long.

It's a helluva cliffhanger going into next week's season finale. Ackley's gone, but Frank and Charlie still must face the music for their flouting of military policy. Since Thin Man must give way to implosion for the Manhattan Project to succeed -- and we know it must succeed -- it will be interesting to see how severe the consequences will be, since the Gadget won't get built without them. What's more important to the military, punishing the breach of compartmentalization or winning the war? Plus there's still the matter of who's been leaking secrets to the Germans. I'm looking forward to seeing all the disparate threads come together.