It starts off interestingly enough, with the Seaview on a useful scientific mission. Nelson, Sharkey, and a visiting geologist, Sprauge (which I keep wanting to spell "Sprague" but I'll go with the credit listing) in Apple 1, investigating a patch of sea bed that seems to be unusually rich in rare minerals, including Idrillium, which is to be used for fueling space vessels. Sprauge makes it clear that he's interesting in the scientific value of the minerals, not their commercial value, which is considerable.
They are proceeding further down for a closer look, when Kowalski interrupts Crane with important news. This is a major absurdity--they would have us believe that a tidal wave has appeared out of nowhere, no warning whatsoever, and is about to strike them. Please. Something had to occur to set off the tidal wave, and if it was that close, Seaview should have felt it. There should also have been warnings screaming over the radio on all frequencies. It would have been a little plausible if Seaview had been suffering a temporary equipment failure--or if there had been an alien or evil genius somewhere in the vicinity who had built an "Insta-Wave" device.
Seaview desperately starts hauling up Apple 1, but of course, it's too late--the wave hits, and the cable snaps. Apple 1 is grabbed from 2,000 feet down and tossed up onto an island. Seaview, on the other hand, which is much closer to the full force of the wave, suffers some damage, but not nearly as much as you'd expect, given the titanic force of a tsunami, and there is no indication that she moved very far from her original position--she just rocked back and forth a bit.
Finding themselves on dry land, Nelson pops the hatch on Apple 1. They hear a strange noise, see an even stranger sight--and hastily close the hatch. Back on Seaview, they do have a nice bit of human reaction. Crane, worried about his friend (and the other two) is fretting and fussing about like a mother hen. Chip Morton supervises the diving party assigned to make outside repairs. The repairs will come to an abrupt halt when the team is attacked by sharks. I realize that this would have been difficult to film, but it would have been so cool if they could have gotten SOME shark footage, rather than simply relying on Chip's statement that they were under attack. (And far more plausible than a giant lizard.)
Speaking of lizards--Nelson comes out of the bell armed with a laser rifle, trying to deal with the creature while Sharkey attempts to repair the radio. At one point, he hits it dead on, right in the eye--and it has no effect. Hitting its armored skin might not have caused much damage, but we should have been left with a very irritated, one-eyed lizard. However, it did cause it to move away, at least temporarily. Nelson and Sprauge leave Sharkey in the bell and go in search of the beach. Sprauge is your basic, garden-variety scientist, not accustomed to this sort of adventurous running around, and he admits quite candidly that he is frightened. Shortly afterwards, he comes in contact with a burst of mist or steam from underground, and becomes...oooh...really mellow, man. Incredibly, Nelson more or less ignores this radical alteration in the man's personality. Some time later, Sprauge drifts away, and Nelson thinks that he sees Crane on the island. Nelson is distracted from "Crane" by the reappearance of the lizard, which has returned to play with the diving bell, knocking Sharkey out in the process.
There is a lovely underwater shot of the Seaview. Crane is still fussing, all the more when he learns of new seismographic readings. A build-up of pressure is going to cause a second tidal wave in about three hours. (This makes their failure to note the first one even more ridiculous.) Sharkey managed to fix the radio, and Nelson calls in to let Crane know that they're...well, somewhere. On an island. With a big lizard. Said lizard cracks the heavy-duty bell with a couple blows of its tail (well, the bell was probably already weakened by the tidal wave) and Nelson and Sharkey make a hasty exit. Crane and Kowalski set off in the Flying Sub to find them. (Presumably they made some calculations to estimate the direction the bell went.)
Nelson and Sharkey find Sprauge, still pretty mellow, and utterly unconcerned that they've been yelling for him, and that the bell, with the radio, has been wrecked. Nelson still doesn't take note of this. Sprauge has seen the image of a pirate beckoning him, and that's all he's thinking about. Sharkey discovers a skeleton, along with a four-hundred year old sword. (The implication is that it's a pirate skeleton, and it's been peacefully lying there exposed to the open air, untouched, for 400 years. Yup.) Sharkey also sees a really bizarre, reddish-pink twiggy thing, and opens fire on it. Nelson and Sprauge saw nothing. The second time Sharkey sees it, he's run out of bullets, and almost skewers Nelson with the sword. It's at this point that Nelson realizes that they're all hallucinating. Oddly enough, it doesn't occur to Nelson that the lizard might be an hallucination, although Sharkey suggests it.
I wouldn't have had a problem having the lizard being an hallucination. Or not having it there at all. Trapped on an island due to be hit by a tidal wave in three hours, and exposed to hallucinogens, could have given them plenty of scope for a wild night. They could all have been trying to kill each other, unwittingly. Crane and Kowalski might have attacked them in the Flying Sub, thinking that they were something else entirely.
Sprauge, led astray by his pirate illusion, ends up in quicksand. (This is a pretty weird scene, because it looks as though Sprauge's hallucination deliberately tried to kill him.) While Nelson and Sharkey are trying to haul him out, Kowalski and Crane each individually react to the hallucinogenic mist, which apparently rises pretty high in the air. (They're coasting at 1,000 feet.) Kowalski's reaction sends them soaring 9,000 feet up in a matter of moments, while Crane's causes them to hit the drink, fetching up against a rather familiar chunk of rock. After recovering, Crane prepares to head for shore, leaving Kowalski to get the Flying Sub running again. You'd expect Crane to suit up and swim for shore, but he ends up rowing a very small rubber boat. Apparently he (and the writer) forgot they were sitting on the bottom.
Lizzie shows up yet again, chasing our heros into a cave. They manage to slip out a side exit and finally reach the shore. Sprauge, who has been dwelling on the imaginary treasure he left at the quicksand pit (this is the same man who expressed no interest in money at the beginning of the show) rushes back to find it, just before Crane arrives. Nelson takes Crane with him to find Sprauge. Sprauge has managed to avoid the quicksand this time, and is hunched over a cluster of roots, insisting that they can't share his treasure. (I flashed on Daffy Duck at this point--"It's mine! It's all mine!") Crane calms him down with a punch to the jaw. There's a odd little bit just here. Preparing to drag Sprauge back to the beach, David Hedison gets his arm around Henry Jones' shoulders, then briefly reaches down with his other hand as though he's about to scoop Jones up in his arms--then remembers that Jones is too big to be carried that way. It's just a moment, but it looks funny.
Back at the beach, instead of leaping into the boat and shoving off immediately, Nelson stands off to one side and decides that the lizard must be destroyed. Did he think it was going to try and swim after them? He orders Chip to prepare to fire short range missiles. The lizard intervenes at this point, in a pretty effective shot, although for some reason the lizard's head looked as though it had some light filtering effect. Nelson orders Crane to shove off, orders Chip to fire at once, and dives for the cave. Rather than some small missile or torpedo, what we see is a huge Polaris missile (you can tell that because it has "POLARIS" right on the side). That missile should have blasted the lizard to bits--not to mention the cave, Nelson, the rubber boat, and least half the island. The beach isn't even marked when Crane comes back, and Nelson cheerfully tosses a few fallen rocks out of his way and and they all head back to Seaview, arriving just moments before the tidal wave hits. The wave that completely obliterates an entire island just rocks the Seaview a bit. Uh, huh.
An entertaining little romp, but it could have been so much more effective.