To begin with, they're in the middle of a storm, with hurricane force winds. Seaview is on hand to assist, if needed, in the rescue of a deep-sea diver who was working with a wrecked atomic submarine. We're never given details as to why the sub was wrecked, if the crew escaped or if they're all dead, etc. Nor is it explained why a single diver was down there. They learn that the naval rescue ship cannot reach the sub because of the heavy weather. Seaview will be needed to rescue Stan Kowalski. Our Kowalski is stunned to hear the news; it had not occurred to him that the trapped diver might be his brother.
I realize that they have to present the stars in an heroic light, but having Crane undertake the rescue all by himself was plain stupid. Aside from the fact that the Captain of the ship should not be taking such risks (all right, Captain Kirk always ignored that rule, too) you should never dive alone--and certainly not at that depth.
(Here's another recurring nit that I'll bring up--the business of divers talking out in the water. It would be reasonably plausible if the divers always wore full-face masks, but they very rarely do, which means that they've got their air hoses jammed into their mouths. The idea that a person could articulate clearly in those circumstances, just by reaching up and pinching the sides of his throat, is ludicrous.)
While Crane is out, Kowalski hears sounds coming from the wrecked sub. Nelson believes that it is the sound of torpedo timers--leaking water might have set them off. He calls to Crane to abort the rescue, but Crane has found Stan, and refuses to leave. He manages to get Stan loose and haul him back to the Seaview, getting there just before the torpedos in the wrecked sub fire. The torpedos barely miss, and the explosions cause heavy damage. Seaview starts to sink. Unfortunately, they're in a deep trench area, and there are no handy ledges for them to land on. Kowalski requests to be relieved from his post--if they're about to die, he would like to see his brother. Chip Morton permits it.
Stan Kowalski is doing pretty well, considering that he was trapped underwater for several hours and ended up running out of air before reaching the Seaview. He puts on a good show of being too tough to die--until he learns that the Seaview is (again!) in imminent peril.
Seaview goes below her estimated crush depth before finally striking bottom--it looked like approximately 4,900 feet. All hands are set to repair duties. Stan insists on having the chance to see the man who saved his life.
Outside communications have been lost. Four banks of output circuitry have been blown. The portable transceivers do not have enough power to get through at that depth. They sent up the emergency telephone buoy (seen in the first season's "Submarine Sunk Here") but the storm snapped the cable. They're completely isolated.
Stan greets his rescuer, commenting that Crane had given him the chance to die twice. Crane and Nelson look rather disconcerted at this statement. Stan thinks that it might have been better all around if they had left him to die--a belief that he repeats when they learn that the air purification system has been wrecked. (Unlike the first season's "S.S.H" episode, they seem to be lacking any emergency air supplies.) Nelson, a firm believer in the "where there's life, there's hope" school of thought, sharply orders Stan to belay that kind of thinking, and go assist with repairs. Stan, a Navy man, almost automatically snaps to attention and obeys. He goes down to the Missile Room, where his brother is already working. Another crewman, Kruger, covertly gives him a dirty look--you can see trouble brewing there. Shortly afterwards, a steam leak occurs, burning Kowalski's arm. Stan justs watches, frozen, as the others rush to deal with the problem. Kruger sneers at Stan, openly blaming him for the situation they're in. Kowalski intervenes, but Stan tells him to get to Sickbay.
With only two hours of air remaining, Nelson has decided to launch the Flying Sub to try and get help. There is no power to launch it--it will have to be done manually. (Actually, it looked like an ordinary launch to me.) FS1 passes by the original wrecked sub. The movement in the water somehow jars it from its position, and it heads for the bottom--aimed straight at the Seaview. Nelson swings the FS1 about (it seems to move very ponderously, possibly because of the depth) and rams the sub, shoving it away from the Seaview. It settles a short distance away (yet another beautiful underwater shot) and Nelson tries to go on his way, but his luck has run out. FS1's engines fail, and it, too, hits bottom, about 100 yards from the Seaview.
While being treated for his burn, Kowalski asks Doc what could account for his brother's odd behavior. Doc points out that such a traumatic experience as Stan went through could indeed result in a change of behavior. (Interestingly, this possible excuse never comes up again for the rest of the show.) It's also possible that Stan Kowalski, despite being an experienced diver, had simply never faced his mortality before. The FS1 needs a stabilization electrode. Crane thinks that they can fetch one for the Admiral, using Stan's special pressure suit. Meanwhile, yet another complication arises--radiation levels from the other sub are starting to climb.
After Crane explains the situation to him, Stan flatly refuses to risk his life. (It doesn't seem to occur to him that, if they can't get assistance, all of them, including Stan, are going to die in short order.) Kowalski, looking at his brother in disbelief, finally accepts that his brother is not joking and tries to hit him. Crane intervenes. He then stalks over to Stan's suit and begins stripping off. Someone has to go, and he won't ask anyone else. Sharkey, apprised of the situation, also attempts to use some forceful persuastion on Stan. Crane obviously is just as disgusted with Stan, but he doesn't have time to deal with it. Faced with everyone's scorn, Stan does offer to talk Crane through the dangerous dive.
Chip Morton is also stunned to find that Crane is going out in Stan's place. They set up the outside camera and a communications link. Sharkey and Morton both simmer with barely suppressed wrath. Stan manages to stumble through his instructions. Despite there only being three buttons, Crane fumbles it as well (under the circumstances, you can't blame him too much.) He makes it to the FS1, hands over the electrode, and immediately starts back. Problems arise again, and when a pipe snaps overhead in the Control Room, Stan panics and tries to run--although there's nowhere to run to. His brother grabs him and forces him back to the matter at hand--getting Crane back inside. Stan really stumbles through the instructions this time. He mentions a helium valve inside the belt (huh?) and then tells Crane to remix his air "with the other controls in the belt". That's nice and precise. Despite the fact that he looks like he's using that top button for nearly everything, Crane manages to make it back. He has a hard time getting his breath back--everyone on board is having that problem.
Nelson fixes the FS1, only now it won't start. The launch tubes are stuck in the silty bottom. Taking an incredible risk, Crane shoots a laser to clear the tubes. FS1 is freed--but she's had all she's going to take. She limps back to the Seaview.
None of the repairs are going well. At least there aren't any new leaks. There is one crazy possibility left, and Nelson goes to carry it out.
With time running out, Kruger's rage boils over, and he tries to attack Stan. Kowalski jumps in, hurting his burned arm considerably, but he holds firm and flattens Kruger (just as Stan had forseen that he could do). With Nelson arriving on the scene, 'Ski attempts to pass things off as a dizzy spell on Kruger's part, due to the bad air. Nelson obviously doesn't believe a word of it, but he lets it pass and sends them off to assist with repairs elsewhere. He then informs Stan that he intends to try swimming to the surface in Stan's pressure suit to get help. Stan is incredulous. Nelson points out that he has to try, even if there's little chance of sucess--they'll have no chance at all otherwise. With only about 15 minutes of air left, Nelson gives Stan a short course in the meaning of courage, including a demonstration when a section of the hull collapses, causing yet another violent lurch. A control panel gives way, and Stan, shoving Nelson out of the way, gets trapped beneath it. Nelson stands fast and gets Stan free, then continues with the business at hand, despite the fact that his hands have been burned and he would have difficulty operating the control knobs of the suit.
Things are popping all over--the Control Room gives off a considerable light display before they're able to cool things down. Sharkey reports that a couple men had died when the section of hull collapsed. Stan reports that the Admiral is just leaving the sub--and they hear the sound of the escape hatch filling. Crane rushes down to the Missile Room. No Admiral, and no Stan Kowalski. Coming back to the Control Room, they spot the diver outside (and I don't understand why; shouldn't he be going straight up?) They watch, horrified, as the air tanks explode and the diver vanishes.
Down to just minutes of air, everyone but necessary work parties are ordered to lie still on the deck. As the gauge drops to the bottom, Nelson comes staggering down the spiral ladder. Stan Kowalski had persuaded Nelson to stay behind with a spanner wrench, going out himself. Which begs the question; what possible reason could Stan have had for saying that it was the Admiral going out? It would have made far more sense if Nelson had told them what he was going to do, only to have Stan clobber him after he hung up the mike.
Suddenly, there is the unmistakeable sound of a diving bell connecting with the hull. Stan Kowalski drops down the ladder. Only one of his tanks had burst, sending him 50 feet starboard before he headed topside. The rescue ship does not seem to have bothered sending down some air cannisters, as they did with the first season's "S.S.H.", which seems pretty ridiculous; they are more or less completely out of air, and there are about 123 men to transport, a few at a time, in the diving bell, which has to go up and down nearly 5,000 feet. By the time it came down for the last trip, the remaining men should have been dead. The last party gets clear just as the first sub explodes. Seaview is left behind, but not for long. Salvage operations will soon be underway, and Stan volunteers to supervise. (Crane looks a little dubious.)
And after that long, exhausting, tension filled episode--we still don't know what Kowalski's first name is! (You would think that 'Ski would be rather irritated at having his brother address him as "Kid" all the time.)