The prologue starts in 1945. There is an intense naval battle going on. Below the waves, a secret Nazi installation is getting rocked by depth charges. Only two men are running the base. The younger man urges that they use their "secret weapon" to turn the tide of the battle overhead, but his commander refuses. The weapon is to be used against the capital cities of the Allies, not wasted on a single sea battle. A further barrage causes considerable damage to the base, and a small cannister falls to the floor, emitting a thick white gas. The two men collapse.
35 years later. Seaview is on, presumably, a routine cruise, when sonar spots something unusual 2 miles ahead. They find a seaweed-covered mound--and Patterson, on the hydrophones, picks up what sounds like a human heartbeat. Actually, they should have picked up two heartbeats, and, if the men were in a state of suspension, those beats should have been extremely slow, if they were discernable at all. An alarm goes off, signalling the presence of mines. (This must have been installed after the 1st season fiasco with the minefield in "Submarine Sunk Here.") Crane orders them into reverse, but of course it's too late. Someone may have jumped the gun with the special effects for this scene--a panel starts to spark off before the ship lurches in reaction to the explosion. Coming back after the credits, there's an excellent underside shot of the Seaview caught up in the aftersurge. The main generators have blown. Nelson hurries down to the Control Room to find out what's going on. There should be no mines in this area, and certainly not at this depth.
They have an hour to kill while awaiting repairs, and, Seaview being Seaview, they HAVE to go take a look at that mound. Crane and Kowalski make the dive. They locate a hatch cover that's not quite hidden by vegetation and make their way inside. Somehow, after thirty-five years, there is still breathable air inside, although it's a bit musty. The entire area, in fact, is musty, dusty, and rusty. (Sounds like a trio of gremlins.) Crane and Kowalski spot a man lying on the floor, dressed in a Nazi uniform. The uniform is smudged with dust, but his face and hair are clean. In spite of the surroundings, Crane and Kowalski think that the man must have only recently arrived there. They are interrupted by the commander, who has revived now that Crane turned the air back on. (The younger man, for some reason, remains unconcious.) With admirable focus of mind, the commander ignores his altered surroundings and concentrates on the two strange men who have somehow gotten on board his base. He announces that they are prisoners of the Third Reich. Crane and Kowalski exchange a "yeah, right" look. Crane thinks it's all a joke, even after the man backhands him. He mentions the thirty-five year difference, which the man utterly ignores. Threatening to kill them, the man suddenly has difficulty breathing. In spite of the fact that he's now breathing fresher air, the gas from thirty-five years past somehow knocks him out again. Crane calls for Apple One to be sent down to retrieve the men, while he and Kowalski gather up some samples from the base--including cannisters of the gas (clearly marked on top with a swastika).
In Sickbay, Doc concedes that they are under the influence of some drug, which he can't identify. The commander awakens. (The younger man is still unconcious.) He looks at Nelson, instantly recognizes him as the top authority in the room, and addresses him alone. He recognizes his surroundings as a Naval Sickbay. Nelson insists on knowing who the man is before telling him anything. The commander formally announces himself: Admiral Baron Gustav von Neuberg. Nelson, with perhaps a touch of reverse snobbery, simply calls himself Nelson. von Neuberg refuses to give any more information until he can consult with his aide. In spite of the comments von Neuberg has made, Nelson, like Crane, assumes the man is playing a joke and doesn't bother to try and persuade him of the passage of time. Crane orders a guard posted outside Sickbay, and he and Nelson leave.
Nelson gets in touch with the British Admiralty, and learns that Admiral von Neuberg was Nazi Germany's top research scientist--and 49 years old at the time he disappeared in 1945. Crane scoffs at the notion that this man could really be von Neuberg, but Nelson concedes the possibility--and mentions the idea of suspended animation. Down in Sickbay, von Neuberg has been studying a plan of the Seaview posted on the wall. Such a plan would, presumably, include the detail of the ship being built in 1972-73, but von Neuberg apparently missed seeing it. He refuses to believe that such an advanced submarine could exist outside of imagination. Doc tries to argue with him, but the aide--Lt. Froelich--at long last awakens and promptly knocks the doctor out.
Nelson's not sure if they're real Nazis, but he is certain that they are there for a purpose. He and Sharkey go down to the base in Apple One to search it. They take note of a plaque marked "June 1945", but Sharkey still doesn't believe it. Nelson wrestles open a closed panel, which immediately spits out a burst of sleeping gas. Back in the Sickbay, von Neuberg and Froelich take out the guards with distressing ease. In spite of the fact that he does not believe in the Seaview, von Neuberg takes the plan with him to use as reference--and he accepts the fact that Seaview has a dangerous weapon on board that he can perhaps turn to his own use. He is supremely confident that the two of them can take over the Seaview--and that confidence is not misplaced, sad to say. While Crane is trying to reach the unconcious Admiral, von Neuberg and Froelich find the Armory and knock out the crewman there. They could destroy the Seaview--but von Neuberg thinks that High Command would like it captured, instead. Going to the Missile Room, they shoot two crewmen and knock out Patterson--who makes a valiant try to disarm them. von Neuberg instructs his aide to remain hidden, while he returns to the base. Surrounded by all this modern technology, von Neuberg only thinks that the Allies are more advanced than they had thought. I think it would have been more interesting if at least one of them had started to think that maybe, just maybe...after all, what would have been the point of the enemy trying to make them think that 30-odd years had passed? There were all kinds of things on board that could have had a date inscribed. They could have remained adamant in front of the enemy, but they could have discussed it between themselves. Not once did they consider the possibility.
Crane discovers the escape, and orders a search. Patterson awakens and calls for assistance. For some reason, although von Neuberg had not yet left, he and Froelich left Patterson alone, instead of knocking him out again. Crane orders five men to prepare to dive with him to the base. Patterson is left alone in the Missile Room (that seems to happen to him a lot). The Nazis prepare to attack Patterson, but are interrupted by the arrival of the five divers. Having found the cannisters of gas that Crane brought aboard, they throw one at Patterson and the divers. They're knocked out--not suspended. von Neuberg prepares to leave, after ordering Froelich to the Armory. He's changed his mind about trying to capture the Seaview--Froelich is to prepare to destroy it. Froelich has no problems in comprehending the mechanisms of the escape hatch, and von Neuberg is sent on his way. There's a bit of bad timing on Crane's part--just as Kowalski's search team would have found Froelich, they are called to join the search closer to the Armory.
von Neuberg arrives at the base just as Nelson and Sharkey are stirring. I find it utterly absurd that von Neuberg did not notice that his shiningly clean base has--in seemingly just an hour or two--degenerated into a filthy, rusted-out mess. I've heard of one-track minds, but this is ridiculous. von Neuberg displays his "secret weapon" to Nelson--a series of missiles, loaded with a new explosive (well, new to him) that will strike Paris, London, Moscow, and Washington. He turns them on--they will go off at 1800 hours that evening. (The elderly missiles tremble quite a bit as they power up.) Nelson finally makes a serious attempt to get the change in time across to von Neuberg, who is having none of it. I don't understand why Nelson did not point to the base itself as clear proof of the passage of time.
Back on Seaview, Crane finds Froelich and shoots him. Froelich shoots him in return, although it's hard to see it at first--it looked at though Crane just hugged the wall, which would be the closest he could come to trying to duck in a corridor. Froelich slips inside a room marked "Automatic Maneuvering Control". (Automatic Maneuvering--you can just see a major Seaview lurch coming up.) Kowalski's team hastens up. 'Ski notes that Crane has been shot--just a nick in the side. Rather than just reaching for the nearest microphone (there should have been one somewhere in the vicinity) Crane sends 'Ski running for the Control Room. Out of breath, 'Ski reports the situation--including the Captain's injury. Chip Morton orders him--as Acting Commander--to get down and haul Crane to Sickbay. Froelich calls over the P.A. system, demanding to speak to the man in charge. Chip, at the moment. He demands unconditional surrender, or he will destroy Seaview in 10 minutes.
In addition to destroying four cities, von Neuberg decides to juice things up a bit by adding cannisters of nerve gas to the missiles, which will destroy everything in a hundred mile radius. He has respect for Admiral Nelson's rank--he has Sharkey doing all the work of hauling the cannisters of gas. Nelson clues Sharkey in with a baseball reference--it's always baseball. While Nelson is explaining this "American colloquialism" to a suspicious von Neuberg, Sharkey brings another cannister and throws it in von Neuberg's lap (Ouch!). Nelson prepares to destroy the missiles, but he's forgotten that, where there's one booby trap, there might be two. He and Sharkey are zapped by an electrical charge.
Froelich (who, at the moment, is showing no sign of being wounded) had managed to close off the vents leading to the Maneuvering Room, so they can neither toss in a gas grenade nor send a crewman inside. Instead, they rig an heating charge to the door. Crane may or may not have gone to Sickbay--if he did, he left as soon as the Doc slapped on a bandage. He's got his ship to worry about. With only seconds remaining, the charge is ignited. Kowalski grabs the knob--which should have been scorching hot--and he and two men rush the room, only to meet an explosion (which somehow doesn't kill them.) Seaview lurches. (Well, we saw that coming.)
Nelson and Sharkey awaken to find themselves tied up. It's 1800 hours, and the missiles...short out. It seems obvious that they were simply too old, but Nelson doesn't try to point this out to von Neuberg. The damage has ruined the base, which is filling with water (which we never see). von Neuberg is utterly despondent--with the failure of his weapons, there's no point in going on. Nelson tries to encourage him that there's still a life to live, if they can reach Seaview. von Neuberg suddenly pauses. Nelson may think that he's succeeded in convincing von Neuberg, but you can see that von Neuberg is thinking of all those weapons on Seaview.
Froelich had slipped out of the room through the vents--and we finally see a hint of his wound--he's favoring one arm. He gets to the Missile Room--which seems to be unmanned. von Neuberg, Nelson, and Sharkey swim back to the Seaview (quite an achievement, considering that they went down in the bell) only to find Froelich there with a gun. (Nelson must be getting pretty tired of this.) von Neuberg announces his plans to use Seaview's nuclear warheads against the capitol cities. (Even if he knew how to aim these modern weapons, there's the little matter of needing four men with keys to activate them.) The new damage to Seaview will take thirty minutes to repair. Crane again plans to take divers down to the base--they somehow overlooked those sizeable explosions down there--but Chip reports an emergency in the Missile Room.
von Neuberg plans to send the lethal nerve gas through Seaview's air ducts. Nelson babbles that the gas will re-route back to them, as he backs up and grabs a can of the other gas. Somehow, this gas does not knock them out completely. The fight scene was quite well done--you can actually see Richard Basehart and the others doing some of their own fighting. Nelson and Sharkey get knocked out. Froelich collapses before he can reach the firing panel, but von Neuberg manages to do so. One missile is launched--and no one seems to hear it go off. Nelson somehow manages to revive sufficiently to grab emergency air packs. He puts one on Sharkey before he goes to the microphone to order interceptors launched. (He should have done that the other way around.) In spite of breathing nice, clean air, Nelson collapses again. No one gets put in suspension this time around, either. The interceptors intercept on cue, Crane and and others get inside the Missile Room and carry Nelson and Sharkey off to Sickbay. They don't bother with the Nazis. We don't actually see Froelich again, but von Neuberg dies and ages--or ages and dies, it's hard to tell. This was also irritating. When the suspended animation ceased, they should have either started aging normally from that point--or they should have commenced aging right away, not at the last few moments. That would have added quite a bit of interest to the situation. A decent enough show--but it had so much potential to be better.