Cha-Ka is strolling through the jungle when a coelophysis comes along to chase him. Further ahead, the Marshalls break for lunch during a survey expedition; Dad lays out a map charting the known pylons. Holly calls out for Cha-Ka while the men speculate on the next pylon's location; following the present pattern of 1/4 mile separation, the next one should be 50 yards ahead. Will insists on eating before moving on, but after he complains about his sister's food preparation skills in general, Holly reveals that their lunch is with their missing Pakuni friend. Holly becomes worried about what could have happened to Cha-Ka, but Dad assures her that he will be safe; the jungle, after all, is his home.

Cha-Ka flees through the dense jungle from the dinosaur, who follows close behind. After he trips, Cha-Ka lay curled up and whimpering on the ground, awaiting a gruesome fate, but a hole miraculously opens in the clearing to swallow up the beast. The Paku looks around for his harasser, setting down the basket to examine the dinosaur's footprints, whereupon the ground dematerializes once again, this time consuming their lunch. Cha-Ka is startled to discover the basket missing, but manages to make contact with the Marshalls.

Will, Holly, and Dad arrive at the clearing to meet the upset Paku. While Holly listens to Cha-Ka's story, Will consults their map to conclude that a pylon should be right in the empty clearing. The clearing's circular symmetry appears to be supportive evidence, but the pylon is nowhere to be found. Holly asks Dad to hear Cha-Ka's tale, since she can't make sense of it herself. In his native language, the Paku reveals how a "gobi" (Spot) chased him, when suddenly "oganza" (magic) happened; the dinosaur somehow disappeared into the ground. Will scoffs at the story, suggesting that Cha-Ka had been nipping at Holly's smilax cakes (is Will admitting that the family knowingly uses hallucinogenic ingredients in their food?), but Dad notices the coelophysis tracks that suddenly stop in the center of the clearing. Will also notices that the lunch basket is missing, which the Paku claims disappeared by magic, too. Will accuses Cha-Ka of making up the whole story, while Holly defends Cha-Ka's claim; Dad arbitrates by asking the little Paku to retell the story once more. Cha-Ka re-enacts the events, receiving more scoffs from Will, but Dad reminds his son that in the Land they are in, anything could happen. Just then, Holly hears a buzzing noise (the electronically synthesized kind associated with dematerializations as a video Sci-Fi rule of thumb) followed by a pit opening up before their eyes. Foolishly the Pakuni boy peeks over the edge, and inevitably he falls in. As quickly as it came, the pit opening disappears; Dad is at a loss to explain Cha-Ka's fate to his daughter.

As the family stares in disbelief, Dad warns his children not to step on the spot in question for it may open back up. Dad makes the unfounded assumption that what has just occurred may be a vital part of "the master scheme of things in the Land of the Lost". He then guesses that the nearest pylon may control the pit, so they refer to their map in order to test his hypothesis. Before they head out, Holly wishes to stay behind, should something happen where Cha-Ka needs their immediate aid. As the men jog over to the pylon, Will mentions to Dad that though he got a good look down the pit (a false statement considering Will's relative position to it at the time), he could see no bottom. Meanwhile, Holly clears away sand above the pit to reveal a smooth surface (the stage floor). A view from below reveals it to be transparent looking out.

On the way over to the pylon, the men almost run into a feeding allosaurus, but with care, they make it safely to their destination. Inside the structure a heartbeat can be heard, though there is no control panel. Dad wildly assumes that this pylon indeed controls the hole. Suddenly, a wobbling green glow appears, through which they see Holly clearing dirt off a disc; next, she ties an anchored vine to her waist and crawls onto its surface. When Holly tries to chip at the disc's surface with her knife, Dad calls on them to rush back for her safety, but before they have a chance to leave, Will sees through the vision that his sister is suddenly gone.

On their way back, Dad and Will once again encounter the allosaurus, and though they get its attention, the beast inexplicably charges off (this was actually a recycled animation scene from "The Stranger", where Big Alice chased off a band of crossbow-firing Sleestak). They return to the clearing to discover the cleared-off disc shut, with Holly's vine passing through it and her knife lying on top. Dad stops his son before he can reach the knife, warning that the disc could open up under his weight. Dad suggests placing a weight on it to force it open, but stops Will from hurling a large rock at it, realizing that it could fall and hurt Holly. Their next approach involves tying a vine around Dad's waist so he can climb down to rescue his daughter, but before the hole opens up, Holly's vine breaks. She tumbles down the shaft (a lame special effect where a fake-looking doll rotates on an unseen skewer, accompanied by the whistling of a falling bomb). Holly then floats in space, orbiting with Spot, Cha-Ka, and the picnic basket around a house-sized, jagged red ball. She calls out to Cha-Ka but soon passes behind the huge pulsating sphere.

Back at the surface, the disc opens up, so Dad prepares to climb down. Will feeds out slack from around a tree, lowering Dad into the shaft. Dad soon finds Holly's broken vine and calls out in vain for his daughter down the shaft. He calls out to Will and pathetically tries to climb out, but the disc promptly closes, snapping off his vine. Dad meets the same lame fate as Holly: an unrealistic dummy tumbles down the cylindrical shaft. Will screams out to his father, pounding and stomping on the closed disc, but all of his efforts prove fruitless.

Orbiting the huge ball, Dad identifies it a "generator or giant heart". He calls out to Cha-Ka and Holly, but they all drift helplessly around the object. The generator's pulse accelerates, peaking in a beam shot at the coelophysis; the dinosaur is then drawn in and consumed. Having witnessed the event, Dad concludes that the generator "must be the energy source for the Land of the Lost"; justifiably, he worries that they may be its next victims. The generator shoots at Dad, but luckily misses; he instructs his daughter to curl up, forming a small target. The next beam reflects off of Holly's signalling mirror (the event strangely sounds like a ricocheting bullet); the close calls gives Dad an idea. With the aid of his mirror, Dad redirects the next beam back to the generator, where its pulse abruptly stops. Holly wonders if Dad has killed it, but its pulse slowly returns along with a growing, swirling wind. The gust begins lifting everyone up, and the next thing we know, they begin climbing out of the opened disc.

Will asks Dad for an explanation to everything that happened, but his father assigns him to help Holly up first. The disc promptly closes once everyone is out, whereupon Will requests the details. Dad describes the ball as a "huge mass of energy, like the sun", and believes it is the main power source for the Land of the Lost. Out of thin air, he postulates how matter, like the coelophysis, is consumed by the generator, converted to energy, and distributed though the pylons. When Will asks why they weren't consumed, Dad mentions how they almost met such a fate, but he managed to give the generator "a case of acute heartburn" ("the biggest burp you ever heard", claims Holly). His sons further questions are stifled when Dad says he'll talk about it later; Dad also recommends they leave the ropes in place to mark the location of the disc. Will lags behind out of curiosity, and in a tacky ending catches their intact basket belched up by the pit.