We're thrown straight into it--the Seaview is on the hunt for a "life form", and thinks that it has been found. Crane and Kowalski go outside to check. Nelson is out searching with the Flying Sub. The creature is a bizarre looking thing that seems to be made up of fronds, and makes a sound reminiscent of metal shrieking. Seaview picks up a dangerously high energy field building in the creature and urges them to turn back. As they do so, they find themselves confronting the creature. Crane is hit by a charge, and sinks to the seabed, paralyzed. Kowalski ducks for cover. You'd think he would attempt to drag the Captain with him, but that wouldn't fit the plot. As the creature approaches Crane, it's obviously a tiny doll dressed in a wetsuit, but Crane's paralysis makes it work pretty well. The creature scoops him up and engulfs him. Chip Morton attempts to call Crane, and, incredibly, Crane responds, if only briefly, saying that he can't breathe. Kowalski fills Chip in on the details. The Seaview comes forward to assist, only to knocked back on her heels by another energy burst. Nearly all the control panels seem to spark off simultaneously, and the Seaview hits (are we surprised?) that outcropping of rock yet again. (At least this time, the whole sequence is viewed from the back, which gives it a touch of novelty.) The main transformer has burned out, and there is minor hull damage. Patterson estimates a 30 minutes repair job, but Chip tells him to make it 15. He then calls the Admiral.
Nelson is travelling with the author of their misfortunes, Dr. King. The implication at this point is that the creature had escaped from them. Nelson is confident that they will be able to find it--and then Chip calls with the dismal news. Apparently the creature had grown enormously from when it was last seen. Nelson kicks into high gear, and rapidly locates the creature. It's at this point that we learn that Dr. King had created the creature, using elements from the sea--and then had deliberately set it loose in the ocean. They spot Crane, released from the creature's grasp, but still paralyzed. Kowalski quickly moves in and grabs him. Nelson interposes the FS1 between the divers and the creature, giving 'Ski time to reach the hatchway. When 'Ski hauls Crane on board, Crane is not breathing, although there is a faint pulse. They give him oxygen and dash for the Seaview.
Crane has stopped breathing again by the time they get him on board. Doc gives him a shot--adrenalin, perhaps--and he begins breathing again. Nelson orders Seaview into a "cruising circle" around the creature as soon as she's capable of it--with every available scanning device in use. He has King join him in his cabin. King expresses concern for the creature's welfare. Nelson coldly informs him that, if Crane dies, he will hold King personally responsible. King protests that there are always risks to take in the cause of science. Nelson counters that stupid risks are inexcuseable. King set the creature free with no controls--and, presumably, no supervision at all. Quite possibly no one knew what he was doing until it got away from him. Nelson announces that he is going to kill the creature. King's protests are cut off by Doc's urgent call from Sickbay.
By the time they arrive, Crane is dead. Doc continues his useless gesture with the air mask a few moments more. King looks at Crane, smiling slightly--the red flag instantly goes up. Crane spontaneously starts breathing again. Doc is astonished--pulse and breathing are perfectly normal, yet he's still in a coma. Nelson is called to the Control Room, but tells King that he wants to see him in the lab. With Nelson gone, King suddenly becomes very strange, speaking of specialized knowledge. He has Doc look at Crane--and Crane's head is suddenly covered by a pinkish, shaggy mask. Doc looks at King, and King suddenly has the same mask. He had accidently touched the creature at some point, and became "one" with it--as Crane now is. Crane abruptly awakens, jumps up, and puts on his shirt--all the while staring at Doc, as does King. Crane makes it clear that Doc is next in line. We get a rare chance to see the doctor's mettle--he jumps to the attack, and gives a pretty good account of himself, but of course it's two to one. By the time he's knocked over the gurney, he's been taken over. And there's more to come....
There's apparently been some passage of time; Chip speaks of several hours, but it's not clear if it's several hours since their encounter, or since they were informed of the whole situation. The creature has apparently doubled in size. ("Apparently", because there is nothing to make its size change noticeable to the audience.) Chip suggests killing it now, and Nelson agrees. Crane suddenly appears, startling them considerably, but happily. King again protests killing the creature, and this time has support from Crane. Quite unusually, Nelson does not exert his authority to insist on doing it his way. Instead, he proposes shooting the creature with tranquilizer missiles, putting in probes and taking samples, and then destroying the main body of the creature. King agrees, and FS1 is prepped. Crane leaves, mentioning that he's going to check the instrumentation "below", which implies the FS1, which made it sound as though he was going to get Chip under control. FS1 is launched, carrying Nelson, Sharkey, and King. We learn that FS1 now has missile capacity. The creature throws a charge, causing considerable damage, but Nelson hangs on and gets the missiles fired. The creature seems to clutch its stomach and keel over. Nelson brings the FS1 under control. At this point, Crane gives a puzzled Chip the con and takes over his position. Doc comes down the stairs, giving Crane a significant look. Crane bids him to return in 15 minutes. Sharkey and King leave the sub and plant the probes in the creature. Calling Seaview, Nelson is startled when Crane responds. He reports that the creature's energy level is "safe". The divers return to FS1 and Crane again reports that there is no change in the energy level. However, when the divers arrive on board, a sudden burst rocks them, and various circuits short out. The creature, fully awake again, grabs them. Oddly, King looks quite apprehensive. Nelson manages to blast his way out.
For no discernable reason, Chip suddenly walks away from where he had been standing. Doc returns, bringing three crewmen with him, and closes the doors between the Control Room and the nose. All of them line up beside the FS hatch.
King is the first to arrive, smiling confidently at the group. Nelson and Sharkey then come up to find the group...all staring at them, and all armed. Nelson, quite reasonably, asks what is going on (in quite a restrained fashion, under the circumstances). Crane tells him that they are "one" with the creature. King moves in. King has a really fine, frightful stare.
Chip and Kowalski suddenly move in through the opened doors. One of the crewmen (not a known face, of course) turns on them...and Chip shoots him. This is where the episode changes from simply scary to horrifying. They've often been faced with the possibility of having to kill some of their fellow crewmen, but this is the first time they actually have to do so. Before sending them off to the brig, Nelson asks for more detail on the creature's intentions. Crane, who seems to have become the creature's spokesman instead of King, tells him that the creature plans to eventually take over all life on the planet. (It obviously doesn't believe in individualism.)
Conveniently, they suddenly have a nice, large brig, rather than the two-man cubbyhole. Kowalski is left on guard--and they really should have told him to stand outside the room. Nelson and Chip don't know how many crew have already been taken over--hopefully, they're all in the brig. Nelson orders all vital areas of the ship sealed off. He and Sharkey head to the lab. Back in the brig, they have a very unnerving shot as the camera pans across the prisoners--all staring intently at Kowalski, without saying a word. Outside, the creature has started moving. Nelson examines a microscopic view of the creature's cells--they seem to be all electrical, either generating or storage cells. Chip calls in, having used the computer to project that the creature is heading for the Pacific coastline, and will grow to the size of a city, with an electrical capacity too high to read. Nelson orders atomic warheads prepared. Back in the brig, they're all still staring...and Kowalski is now starting to react. Kowalski slowly, reluctantly, moves forward...straight towards a row of outstretched hands, which gets my vote for the creepiest moment of the show.
The missiles, having been fired, connected with the creature, but somehow did not explode. We're never given any explanation for this--it might have been that the creature was able to neutralize them with its energy, or perhaps one of the men in the missile room had deactivated them. Meanwhile, Kowalski unlocks the door to the brig, and they head for the arsenal, stopping along the way to pick up a torch. They come to a door and start burning into it. King heads for the lab to start breaking in there, taking Crewman Ray with him. It gets a little confusing at this point as to just where they are--Chip, while informing Nelson of the escape, tells him that they are amidships, trying to break into the Control Room--yet Patterson will report that someone is trying to get into the Missile Room, and Crane will later tell Kowalski that he has to finish cutting through the door to stop Nelson from reaching the Flying Sub, which would seem to imply that they're working on the lab door. Nelson flatly gives the order to shoot the men if they suceed in breaking through. Interestingly, no one really reacts much to this necessity.
Patterson (who for some reason is all alone in the Missile Room), having reported someone trying to break in, is instructed by Nelson to hit the emergency power cut-off. This forces Crane's men to use portable cutters, which will take much longer. Back in the lab, Nelson prepares to test his theory of fighting power with more power. Although he does not comment on it, the sample is noticeably larger than it was the last time we saw it, which is a nice touch. Nelson uses a pair of rheostats, and zaps the sample out of existance. Nelson plans to charge up the hull of the Flying Sub, using two A33 atomic power generator packs. Nelson orders Patterson to collect two packs and swim outside to meet him at the Flying Sub. Crane and the doctor have been listening in on this conversation. (No privacy on a sub.) Crane goes aft. He doesn't say why, but it quickly becomes obvious that he's converting more crewmen. One of them slips into the Missile Room. Patterson spots the opened vent--but for some reason, assumes that the person is still inside. He tosses a gas grenade into it--and is promptly hit from behind. The fight sequence was well shot--they keep the faces fairly well hidden, and Paul Trinka can be seen in an action close-up. One big question about this fight, though--it's clear that the business of being "taken over" is done through touch--and there was a heck of a lot of touching during the fight. So why wasn't Patterson taken over? Patterson is thrown down and a set of shelves pulled over him. The crewman jumps to open the door, but Patterson manages to pull a gun out of a box (conveniently loaded) and shoots him in the back. He stares at the fallen crewman with a grim expression, but not a particularly remorseful one.
Back in the lab, Nelson decides to use the rheostats as a weapon for Sharkey. He yanks open the lab door, clobbers Ray with a stool, and knocks King off balance before fleeing down the corridor, leaving Sharkey to confront King. Nelson quickly arrives in the Control Room, and closes the doors before going down the FS hatch. Chip calls Patterson, who's already suited up, and tells him to get going. Patterson, who can tell that they're about to break through the door, tosses another gas grenade in that direction. Three more crewmen (Crane's been busy) come in, and collapse. Patterson almost gets the escape hatch shut, when Crane suddenly grabs it and yanks it open. He and Patterson start wrestling.
In the lab, King has started up his high-power stare again, and Sharkey begins to react to it, getting sweaty and sounding frightened. King is persuasive, and Sharkey starts to drop his hands. King moves in, and Sharkey, with a final effort, touches the rheostats together--and King disappears. Patterson reaches the FS1--first you think it might be Crane, because he comes aboard and then just stands there as Nelson speaks. Then it seems as though he's been taken over--he looks as though he's in a daze. He haltingly explains that he had had to strike Crane down with a wrench...and he thinks that he killed him. Nelson's a little tight-lipped, but he doesn't have time for remorse, there's too much to do. Patterson takes the power packs and goes back outside. Chip reports that the Control Room is still secure. Patterson comes back on board--you have time to think that he got those packs attached very quickly--and then you notice that the camera is not going above his shoulders. The diver steps behind Nelson and starts to throttle him. It's Crane, not looking as though he has a mark on him. (This leads one to speculate that if the creature was able to heal and revive Crane from a serious clout on the head, perhaps the shot crewmen were spared, as well. If the creature's planning to make everyone "one" with it, it shouldn't distinguish Crane as being worthier than the others.) Nelson manages to pull free, but he's having a hard time of it, until Patterson comes on board and jumps in, pinning the Captain's arms while Nelson knocks him out. (Most unsportsmanlike, but under the circumstances, we won't quibble.)
Crane quickly revives (more of the creature's influence?) but he's securely tied to a chair. He tells Nelson that if Nelson kills the creature, Crane and the others will die as well. Nelson gives a snort and doesn't bother to answer. The creature lets off a burst of energy and the FS1 tumbles. Nelson gets it back under control and, with some really magnificent shots, the FS1 swoops along the bottom and rams full tilt into the creature. The impact knocks them all out briefly, but Nelson pulls himself together, steps to the back of the sub (where Crane is now struggling violently) and sets off the power packs. The creature vanishes in one great burst of energy. All the taken over crewmen promptly collapse.
In Sickbay, Crane seems concerned about his own recovery, despite the fact that all the others are now fine. There is a big cop-out at this point that bothers me. Being told that King is dead, Crane asks if he would have returned to normal if he had lived. Nelson says that King was never normal in the first place--and Sharkey chimes in that, if he had been normal, he never would have used the creature as he did. Sorry, but the creature was using King, not the other way around. King clearly stated that he had touched the creature by accident--and it was surely the creature's influence that made King release it unsupervised into the ocean. King's scientific dreams were no different than many other scientists on this show; there's no reason why they couldn't have presented him as a misguided man tragically cut down--just one of the risks that he himself spoke of.
Crane again demands reassurance that he's all right. Doc points out that the creature's influence vanished when it was destroyed--fortunately; no telling what would have happened if it had somehow managed to survive within its converts. Crane states matter-of-factly that the Admiral would have thought of something if it had. Nelson laughs off this suggestion...but we all know he would have, don't we?