The Seaview is being buffeted about by underwater explosions due to the eruption of an active volcano. Dr. Turner (Victor Jory) is aboard to stop the eruptions. However, his true mission is to bring up ""elixir stones."" An alchemist, Turner needs the stones to keep him immortal. However, in order to bring up the stones, he needs to stimulate the volcano into full eruption!

The Seaview crew is being entertained by puppet cairactures of the Captain and Admiral, compliments of Professor Multiple. Multiple remains on-board when the sub departs, and his dolls soon come to life, replacing their real-life counterparts. Only Nelson and Crane avoid capture and transformation. Multiple boasts that he and the others are all puppets, created by machines from the future that have traveled into the present, and need the Seaview as a new host body. Can Nelson and Crane overcome this fantastic threat?

"Those who see the Flying Dutchman never, never reach the shore." Investigating the loss of Navy ships, Nelson finds an ancient dagger in a cave on an uncharted island, and falls under a strange curse. Haunted by visions of skeletons and an anachronistic ship, he has trouble convincing the crew of his sanity. Meanwhile, Seaview is sailing in circles, and the visiting Commander Van Wyck seems to have disappeared. Guest star Warren Stevens also appeared in "The Saboteur" and "Deadly Invasion".

Aliens snatch a manned space probe launched from Seaview with Chip Morton aboard, and transport it at the speed of light to their observation post on the rocky, unstable surface of Venus. Checking out the duplicate capsule, Crane suffers the same fate before he even has time to launch. With Chip blinded and a prisoner, and the planet's surface due to undergo catastrophic quakes in a few hours, the odds seem to be against the two men.

"There's nothing to do here but to keep from disappearing." Lt. Commander Morton Seaview is carrying a new missile, and Nelson has orders to deliver it to its launch site at all costs. Unfortunately, the missile malfunctions, and Nelson can't get into the sealed silo to fix it. Soon, the crew starts to disappear, and bizarre phenomena plague the ones who remain.

In an attempt to control the planet's tides, Dr. Randolph Mason (a nut if ever there was one -- he is part scientist, part make-up artist!) has invented a powerful electromagnet and established a magnetic field around the moon. The only person who seems to recognize the obvious danger in this silly plan is Harriman Nelson. At first glance, it would appear that Nelson has killed Dr. Randolph. At second glance, it would appear that Captain Crane has betrayed the Admiral. On third glance, the moon is getting closer and closer to Earth, and will soon collide with our beautiful blue orb -- unless the Seaview can save the world. Again. * In this episode, we learn that Chief Sharkey attended Lincoln High in Coney Island, Brooklyn, New York. (There actually is a Lincoln High in Coney Island.

Doctor Blanchard has created a device to control the actions of a white gorilla. Unfortunately, his assistant Leo Brock wants the fame that the inventor of such a device would gain. As a result he uses the device to enrage the gorilla and kill Blanchard. Nelson gets there too late to save Blanchard, but the gorilla is taken on board. Brock sets the gorilla free and he runs amock until both Brock and the gorilla are killed.

A man from the future sends two androids back in time to kidnap Nelson from Seaview in order to add him to a collection of other famous military figures abducted from various eras of the past. The plot of this episode is virtually identical to the plot of the ""Time Tunnel"" episode entitled ""The Kidnappers"".

Seaview is on the lookout for an enemy sub and its underwater sub-pen. Sonar picks up a contact. The rogue sub fires at Seaview, which is saved only by virtue of her new electronic hull shield. Not so fortunate is Captain Crane, who has just located the sub-pen while on patrol in the FS-1. A powerful laser fires a beam at the Flying Sub, crippling the ship. Running out of air, moving in and out of consciousness, Crane is unable to give the pen's coordinates to Nelson. Thanks to the hard work of some enemy agents aboard, Seaview seems unable to rescue the Captain. Worried about Crane trapped in the Flying Sub, Admiral Nelson is particularly impatient in this episode. He constantly barks at Morton and the Chief.

A scientist experimenting with plant life on a remote island has run into trouble. A shore party from Seaview arrives only in time to hear his dying warning that the world will be taken over in eight hours. Nelson brings aboard the only unusual thing he can find -- a red orchid, which proves to be a malign alien (that proceeds to take over his mind and those of the crew).

finds herself suddenly out of touch with the rest of the world, in the wrong part of the ocean and encountering strange creatures. It seems she's been thrown a million years back in time. Then the Admiral opens his cabin door and finds himself back in his Santa Barbara office, confronting the strange Mr. Pem and his pocket-sized time machine, and has to play a risky game before time can return to its normal course. The early part of this episode contains two astronomical errors. First, Nelson takes snapshots of the eclipse-darkened sky with an ordinary camera, but when the shots are developed they show galaxies and nebulae that could only be seen with a telescope. Second, the Admiral describes the pictures as showing 'constellations'. Henry Jones (Pem) also appears as Sprague in "Night of Terror" and once again as Pem in "No Way Back". This episode features re-used footage from "Thing from Inner Space".

The Seaview is en route to rendezvous with the fleet when Sharkey reports a missle fuel leak. Crane and Morton believe it's worth returing to port to repair, however Nelson knows how to handle it. Taking a small breathing device with him, the Admiral locks himself in the compartment in question to effect repairs. However, he drops a wrench, the circuts blow and Nelson is knocked out. When he comes to, he's gripped by paranoia which worsens with each passing minute. Trusting no one, Nelson loses his grip on reality, arresting Doc, fighting with Sharkey and finally launching a nuclear missle at the fleet!

Seaview has been sent to the ocean floor by mysterious pressure impacts. Crane, Sharkey, and Kowalski go out in the Flying Sub to investigate. They, too, are sent to the bottom of the sea. Strange creatures (half men-half fish) present themselves and explain that they intend to take over Seaview (who doesn't?) and eventually the world! Don Matheson starred as Mark Wilson in Land of the Giants.

The ghost of Blackbeard is alive and well, and he wants the Seaview and her crew. The pirate 'drafts' Kowalski, who makes a very convincing and quite blood-thirsty buccaneer. Nelson and Crane have their hands full trying to protect the President of the United States (a guest of a Middle Eastern Shah on a nearby yacht), and regain control of their ship.

About the plot . . . Um . . . Well . . . Uh . . . Okay, here it is: You see, there are these twin leprechauns, one good, the other icky. The icky one wants all the gold that's buried beneath an underwater defense installation in the Irish Sea. The good leprechaun does his best to stop his evil brother from doing any harm . * Footage of Morton and Kowalski trapped in an underwater cave was borrowed from previous episodes. So what else is new? * Why this episode wasn't broadcast on St.

A lobster-like alien emerges from a capsule retrieved from the ocean floor. He claims that all he wants is one of Seaview's nuclear rods to power his ship for the homeward journey, but neither Captain Crane nor Admiral Nelson is convinced he can be trusted. Victor Lundin also played the neck-braced Hansjurg in Season 2's "The Menfish".

Poor Captain Crane. The things he had to go through. This time, he's in the Flying Sub, when he receives a distress call from the Seaview. He comes back to his sub, only to find it abandoned -- again. But wait, there's a force-field on the spiral stairs which knocks Crane out, and there's a stranger aboard who naturally shoots at him. Eventually Crane sees the crew, and he hears the voice of Nelson calling him a traitor. It takes about an hour, and a bullet in the shoulder (fired by guess who?), before Crane discovers aliens are testing the human race.

"But that's not the goal of a man -- of a scientist!" Admiral Nelson At an experimental station in the Antarctic, the crew discovers a 'tropical paradise' -- but most of the scientists are missing. When two unconscious survivors are brought aboard Seaview, something deadly starts to stalk the corridors. Meanwhile, the temperature outside is still rising .... * The white furry monster costume also appears in at least one Lost in Space episode.

Naval ships have been disappearing, and Seaview is on a hunt for the undersea installation responsible. They find a sea-lab that is not only well-armed but surrounded by overgrown and ferocious sea-creatures. To complicate matters, the guest expert aboard is a traitor. Various "dangerous denizens" of the deep from earlier episodes reappear here, thanks to re-used footage: there's a whale, and one of those globular-eyed bottom-dwelling monsters seen in such episodes as "Deadly Creature Below".

"You had no right -- no right to make that second dive without orders from me!" Nelson to Crane Another scientist with another artificial atmosphere (see Season 1's "The Condemned") that will revolutionize deep-sea diving. When will Admiral Nelson learn! Naturally, Captain Crane is used as a guinea pig for these dangerous experiments. And there are fatal side-effects. * A great Nelson/Crane argument takes place in the Admiral's cabin after the Captain has made his unauthorized second dive. * In this episode it is not Nelson who shoots Crane, but rather, Chip Morton. * Notice the tears of gratitude and relief in Crane's eyes after Nelson gives him the antidote at the very end of the episode. * Crane also shed a tear (from pain) in Season 3's "Day of Evil".