The episode starts with a mishmash of disaster clips--bright, clear shots, antique footage, and some that was just...there. Earth is facing worldwide devastation, and the source appears to be a strange cloud. Captain Crane has been sent in the Flying Sub to investigate the cloud--which actually looks like the aftermath of a nuclear explosion. Nelson cautions him to avoid direct contact. We learn why when Nelson gets a call from Washington. (We could assume that the man speaking to Nelson is the President, but it's never specified--he could be some government scientist for all we know.) In the past three weeks, ever since the cloud appeared, they have sent a dozen ships and planes into the cloud, only to have them vanish. Nuclear weapons have also been fired into it, to no effect. They now calculate that the Earth has only 24 hours before it's destroyed completely. Seaview, Our Last Hope, has been sent in--using only a skeleton crew, as it may be a suicide mission. (This makes little sense, as they make it clear that everyone is going to die if a solution is not found. In addition to which, in the episode "The Shadowman" Crane indicated that Seaview is not designed to operate with only six men on board. In this episode, where the physical hazards are much greater, having only six men on board is ridiculous.)
An underwater quake rocks the Seaview. At about the same time, Crane loses control of the FS1 and gets yanked inside the cloud. Sparks fly, Crane loses conciousness, and there is a sudden, startling shot of what looks like an ugly metal statue behind Crane. Meanwhile, the Seaview is caught up in a lot of turbulence from the quake. Kowalski is sent to check for damage, while Nelson reports in to Washington, to let them know that they're about to move in underneath the cloud. Washington reports back that about half the major cities in the Southern Hemisphere are in ruins. (Why only the Southern Hemisphere? The damage is supposed to be world wide. It's as though they suddenly switched over to the episode "The Sky's On Fire".) Seaview suddenly goes dead in the water. There are no sonar readings, and they've lost contact with Washington. Looking out the nose, they see the cloud in front of them--even though they're underwater. It actually looks as though they're surrounded by the cloud, but Nelson states that there is some sort of barrier keeping them on the outside looking in. Kowalski reports that there is no damage--unless you count the fact that everything is nonfunctional. Nelson, exasperated, orders 'Ski back to the Control Room. They will commence studying the cloud with all scanners as soon as they're capable of doing so.
We see Crane, frozen at the controls of the FS1--and then he suddenly seems to wake up. He calls the Seaview just as they catch sight of him, and reports that everything's fine, and he's coming back. The FS1 somehow slips right through the barrier at the outside of the cloud, and berths. Crane comes up to the Control Room, ignoring Chip Morton's anxious inquiry. He says that he's all right, that the interior of the cloud is simply a whirlwind. He had gotten knocked out by the turbulence, then woke up and came back. Chip protests that the worldwide devastation makes it clear that there's more to the cloud than just wind, but Crane angrily assures them that the cloud is not responsible. Of course, he doesn't have an explanation for what IS causing the trouble, or why this whirlwind cloud has been sitting in the Pacific for three weeks. Nelson tells him to fetch the film that he shot. Crane at first doesn't know what Nelson is talking about, then makes a quick recovery. Chip is certain that something is wrong with Crane, but Nelson brushes it off. Chip is about to follow Crane down the hatch, but he and Nelson are both called over by Sharkey to check the heat sensors. Down in the FS1, Crane removes the film magazine--and then sets it on fire merely by looking at it. It becomes clear that Chip was right.
There is a brief (and unnecessary) scene from Washington, as the two men dwell on the problem. Every available transceiver is straining to hear from Seaview--Our Last Hope.
Down in the FS1, "Crane" is joined by a metal statue. It claims that "they" (the Seaview crew) suspect nothing. (Apparently he wasn't paying attention to Chip.) "Crane" notes that they can't keep up the pretense for long, but then, they won't need to--the Earth will be gone in a few hours. Meanwhile, these humans have some small scientific attributes that the aliens are unfamiliar with--they want to study them. The metal alien leaves "Crane" to it and vanishes. Up in the Control Room, the scanners read that it's 50,000 degrees Fahrenheit outside, hot enough to turn practically anything into a gas--and yet the Seaview is intact. "Crane" comes up and listens as the crew discuss the cloud. Nelson speculates that the intense heat generated by the cloud could result in all the natural disasters going off everywhere. "Crane" slips out of the room. Suddenly realizing that Crane has been gone too long, Chip goes down to the FS1. Nelson, meanwhile, proposes to break through the cloud's barrier using heat-seeking missiles, and sends Sharkey to prepare them. Sharkey has a quite reasonable question--breaking the barrier will presumably expose them to the full heat, and what happens then? Nelson elects to ignore this. Down in the FS1, Chip finds Crane missing and the film being burned. A suddenly lurch rocks the Seaview, and sets things on fire in the FS1. Nelson and Patterson rush to the rescue.
Kowalski, passing down a corridor, is knocked out by "Crane"--for no good reason that I could see. Crane goes back down the corridor and enters the Circuitry Room (a prime area for wreaking havoc). Chip, having recovered from the smoke and such, tells Nelson that the film magazine was burnt before the fires started. It starts to dawn on Nelson that Chip had been right about Crane. He sends Patterson to look for Crane--he's got to be somewhere on the sub. All the power abruptly comes back on, and Nelson dryly suggests to Patterson that he try the Circuitry Room first. The implication here is that "Crane" was responsible for getting things back in order--but then he starts messing things up again, leading to Sharkey nearly getting crushed by one of the torpedoes. Patterson finds Kowalski unconcious but reviving (ever notice that unconcious people always come to just as someone finds them?) Kowalski seems to be pretty shaken up--he tells Patterson that he was on his way to the Circuitry Room when he was knocked out--but he was travelling away from the room when "Crane" hit him. Patterson assumes that 'Ski had been knocked out by the most recent lurch. Another lurch follows up--but Patterson recognizes that it was not caused by a quake. More like someone messing around with the controls. Patterson is right on the mark. Chip reports that the controls seemed to have been "taken over" temporarily, but they're all right now. Sharkey needs help in the Missile Room (that's what you get with only six men on board) and Nelson goes to assist. "Crane" has overheard this, and when Patterson and Kowalski find him and tell him he's been ordered to the Control Room, "Crane" tells them to follow him to the Missile Room instead. Not wanting to argue with a superior, the men obey.
In the Missile Room, "Crane" calmly belays the Admiral's orders to fire the missiles. Nelson comes in in time to overhear this. After a brief exchange, Nelson orders Sharkey to arrest Crane. "Crane" starts tossing the men aside like pesky flies. Nelson asks him to identify himself. "Crane" responds with "Commander Lee Crane", but Nelson has become convinced otherwise. "Crane" abruptly gives up the pretense, and says that they are helpless against "us". Nelson pulls out a gun. "Crane" turns and gestures at the torpedoes. (Here, and in the Circuitry Room, David Hedison has been having a fine old time with his gestures--he looks like a particularly exuberent musical conductor. One almost expects to hear a burst of music rather than the sparks and explosions.) One of the torpeodes disappears. Nelson shoots at "Crane", to no effect. (As usual.) There's not even any bullet holes in his shirt. "Crane" knocks them all down (and, with Nelson and Sharkey, out as well.) He retrieves the gun and orders Patterson and Kowalski out of the room. Standing over Nelson's recumbent form, the image of Crane morphs into a metal figure, before both he and Nelson vanish.
Patterson and Kowalski come to the Control Room to report the emergency in the Missile Room--but falter as they do so. I thought at first that Kowalski was just being unusually inarticulate, but then it becomes clear that their memories of the incident are slipping away. Chip takes their word that "something" is wrong, and has them arm themselves. Getting no reponse from the Missile Room, the three head down there. Sharkey comes to, to find "Crane" and Nelson gone. He's unable to clearly remember, either. Chip knows his duty, and sets them to setting up the torpedoes as ordered by Nelson. (Finding a torpedo missing only causes them to pause a few moments.)
Nelson finds himself wandering in mist. A voice speaks to him. It says that it is visible--Nelson just doesn't want to see. It takes on its metal form--which isn't its true form, only what Nelson is capable of comprehending. Nelson asks why it's being so considerate of his feelings. The alien states that Nelson (and the others) are "an unusually interesting specimen of human". They want to make a study before they finally dispose of them. He shows Nelson what looks like an image of the Sun's surface, and says that it is his world. They are here on Earth to mine it, and never mind that the mining will result in the Earth's destruction. I really wish the episode had gone in another direction at this point. They were indicating some interest in Nelson and the others. I know that Irwin Allen preferred direct, explosive action, but it would have been interesting if Nelson had tried to argue on behalf of the Earth, both in the cloud and back on the Seaview. For example, why destroy an inhabited world when there must be thousands or millions of uninhabited worlds also rich in minerals? Instead, Nelson simply states flatly that he intends to keep trying to thwart them--which the aliens will find amusing to watch. This puny human thinks that he can match wits with the Masters of the Universe? (Incidently, I wondered just what the other alien races Seaview has encountered would think of that moniker. I rather think that they would take exception to it.) Before returning Nelson to the Seaview, the alien shows him Captain Crane--presumably unconcious, with a clear plastic bucket over his head. They're examining his mind. Nelson suggests letting him come back so that they can at least die together.
Nelson appears in the empty Control Room. Repeated calls get no response from the remaining crew. Nelson collects a laser pistol and leaves the room. "Crane" appears and follows after. Nelson checks out the Circuitry Room, then heads for the Missile Room, with "Crane" following. It's clear from "Crane's" expression and behavior that it's not the real thing. Once in the Missile Room, however, "Crane" sounds normal--and acts as though he doesn't know what's been going on. Nelson remains suspicious. Suddenly, Sharkey is standing at the torpedo controls--just as he was before--following the Admiral's orders. "Crane" belays the orders--just as before. Nelson, understandably, looks confused and shaken--it's like a major case of deja vu. This time, however, "Crane" has only countermanded the orders until they can get the automatic timer locked in. He gives Nelson an innocent, "What were you expecting?" look, and sets the men (Patterson and Kowalski have also poppped up) to loading the torpedoes. Nelson decides to return to the Control Room. He finds Chip there. Chip seems unaware of any time lapse since the Admiral originally left the room--he just had a brief dizzy spell, probably from the quakes. Nelson is about to confide what he really thinks, when he's interrupted by Sharkey, telling him that the torpedoes are ready. Nelson orders Chip to be ready to move into the cloud at flank speed if they manage to break through. "Crane" himself launches the torpedoes. This, of course, results in a major lurch. "Crane" stands quietly as Sharkey, Patterson and Kowalski get knocked about the room.
Chip Morton is the only concious human on the ship. Down in the Missile Room, the second metal alien reappears. They now have the Seaview's weapons to study. (One wonders why these self-proclaimed "Masters of the Universe" need to study Earth's weapons at all, when they obviously have so much more power readily to hand.) The alien (presumably the leader) orders "Crane" to give them 20 minutes--then the damage to Earth will be irreversible. (They interpose another pointless Washington scene--they calculate they have 30 minutes until the end of Life As We Know It. They also yell for the Seaview, Our Last Hope, to no avail.)
Chip yells for help from anyone--the Admiral is badly hurt. Unfortunately, the only one who hears is the last one we can expect any help from. Chip takes a full look around with the periscope, then jumps into the driver's seat. "Crane" walks in, and asks why he's not assisting the Admiral, who's apparently taken a good jolt of electricity. Chip responds that he's following the Admiral's orders. "Crane" bends over Nelson, then asks Chip what Nelson was planning to do once he was inside the cloud--but Chip doesn't know. "Crane" starts to throttle Nelson. (David Hedison didn't really put his heart into it, which may explain why they quickly changed camera angles. Maybe he just didn't like the idea of strangling Richard Basehart.) Chip sounds as though he's suddenly realized what the Admiral's plan must have been--he starts to speak of the missiles, then realizes what "Crane" is doing. He jumps to the attack. "Crane" yells "Don't touch me!" and really sounds peculiar saying so--not angry or scornful, but almost frantic, as though Chip was getting fresh with him. Chip tears a sleeve loose--revealling metal underneath. (The "Masters of the Universe" did a rather shoddy job disguising one of their own--they only did the face and hands properly. It would have been more effective, I think, if Chip had managed to knock him into a panel and caused a tear in the skin, rather than the clothes, showing metal beneath.) Chip now realizes the truth, and snatches out a laser pistol. "Crane" is scornful--until Chip hits him in the shoulder. There's no visible damage, but he clearly reacts to it. "Crane" zaps one of the panels with another flamboyant gesture--looking back at Chip to make sure that he sees what the "Master" is doing. "Crane" leaves the room in the ensuing lurch. Nelson, electricuted and throttled, wakes up none the worse for wear. Chip starts to tell him about the false Crane, but Nelson overrides him, having already guessed. The aliens had tried to wipe his memory and failed. (Don't know why--they had no problem with Patterson and Kowalski. But, of course, Nelson is Nelson.) Nelson plans to fire off every missile they have on board. "Crane" goes back to the Circuitry Room, while Sharkey calls for assistance--Patterson really got battered by the lurching, quite probably breaking his arm. Chip calls down that Nelson is on his way--and stand by on the missiles. The missiles get prepped, but "Crane" makes yet another gesture at the Circuitry panels, this time shorting out the firing mechanism. Chip keeps "Crane" from causing any further damage, but he moves in too fast and gets himself knocked out. Nelson sets up the panel for manual firing, and has Kowalski set the missiles for a one minute delay in detonation. Sharkey informs the audience that they are all going to die when the missiles go off, being so close to them. Nelson only hopes that the Earth will benefit. "Crane" turns up to tell them they've been wasting their time--the aliens had only let them live long enough to learn about their nuclear weapons. He knocks the men all down again--favoring the damaged arm as he does so. He prepares for his final gesture--and the missiles go off. Apparently the aliens' existance was tied to the cloud, because "Crane" slowly staggers and collapses.
Sharkey wakes up, feeling, quite reasonably, that they must have failed, because they still exist. There is no explanation for how the Seaview managed to survive. They spot the fallen alien--now back in his metal shape--and Nelson takes that as proof that they succeeded. The alien suddenly morphs to the real Crane, which makes no sense at all. It was clear that the real Crane was in the cloud, having his mind studied--so he should have been destroyed with the cloud. Nelson doesn't seem inclined to inform the confused Crane what has been going on. He goes off to prepare his report for Washington--if anyone will believe it. More to the point--if anyone is there to read it at all. This episode has the same problem that they had with "The Sky's On Fire", only more so. There has been incredible devastation. Millions have undoubtedly died, and millions more will do so in the aftermath of famine and disease. The damage would probably take a lifetime to recover from--and it will all be tidied up by next week. They should not have presented the damage as being so overwhelming, but of course, they always have to have the nick-of-time resolution, no matter what problems it causes. This is another episode that could have been so much better, instead of merely "adequate".