The Pakuni perform a ceremony involving a huge dinosaur egg placed upon an altar. Ta raises a spear above his head, chanting with Sa in their native tongue. Sa hands a small bowl to Ta, who brings it to Cha-Ka after blessing it by the altar. Reciting "hiroshi esishu", Ta dips his finger into the bowl and dabs some of the white paste onto Cha-Ka's forehead. Meanwhile, Big Alice patrols the Lost City plaza.

Cha-Ka arrives at High Bluff and is greeted "me tobi ye" by Holly and Will. The Pakuni boy carries the feathered ceremonial spear as well as a pouch of magic tokens on a belt. When Will, who is working on their pylon map, asks Cha-Ka about his get-up, their little friend replies "oganza bimichi" (translated literally, "magic big-man"). The kids ask him to explain, but Cha-Ka simply responds with "hiroshi esishu" (the Mark of the Test). Cha-Ka then refers to a ceremony, leading Will to realize that the Pakuni boy is passing through a rite of manhood. Further probing reveals that Cha-Ka must steal one of Big Alice's eggs, which worries Will and Holly. For a moment Will tries to explain to Holly that the test of manhood is by its nature dangerous, and the next thing they know, Cha-Ka is gone.

Will chases after Cha-Ka through the jungle, but the clever little Paku manages to hide in the foliage. After Cha-ka continues on, Holly comes searching, too, finding a loose feather from the ceremonial spear and tracking both the Paku's and her brother's footprints in the sand. As Cha-Ka arrives at the Lost City, Will realizes that his little friend must have gone there, so he begins the trek over to the ruins.

Cha-Ka locates the egg (which is about 5 feet long and over 2 feet thick) and begins rolling it to the left edge of the plaza. Holly calls out to warn him about Big Alice, who has noticed her egg being stolen and begins stalking the thief. Will hears the allosaur's angry roars and hurries on to get there. Just as Big Alice is about to close in on Cha-Ka, the Paku quickly empties the contents of his pouch (large shiny chunks of iron pyrite) and nervously calls upon their magic to protect him. Strangely, the glittering ore does charm the beast for a moment, but Big Alice soon reverts back to her angry old self. Like far too many chased-by-monster scenes, the allosaurus takes her own sweet time going after Cha-Ka, simply bellowing more than anything else, yet when Holly urges him to run for his life, Cha-Ka ends up falling before he can clear the plaza. Will pulls out his signalling mirror to shine into Big Alice's eyes; he saves their little friend just as the beast was about to chomp him. Holly yells for Cha-Ka to escape while he can, but the determined young Paku runs back to get the egg. Will continues to frustrate Big Alice while Holly badgers Cha-Ka to flee, but the Paku doesn't appreciate her concern, in effect telling her to "get lost". As clouds begin to block the direct sunlight, Will's mirror trick runs out. Holly grabs Cha-Ka's hand and pulls him along to safety in the jungle, but Will is forced to hide (still significantly exposed) under a log. Though she pokes her head around right near Will, Big Alice inexplicably doesn't find him (can't she smell?). Will, Holly and Cha-Ka join up, keeping their distance from Alice as she patrols the bordering jungle.

Not after long, Cha-Ka is at it again; this time he uses a large leafy branch as inappropriate camouflage against the stone-paved plaza. It appears to Will at first that Cha-Ka is going to make it off the plaza with the egg, but Big Alice inevitably hears it rolling. The kids rush to Cha-Ka's side and help him along with the egg; again Alice stands threateningly close but does little more than bellow. Only after they manage to reach a square frame of closely spaced pillars does Big Alice lunge at them; they stand the egg up to fit it between the pillars and just barely escape from the furious allosaur's jaws. The angry beast is unable to fit its head through, so for the moment, the thieves are safe. The space enclosed by the pillars houses dusty steps leading to sealed doors; it appears to be an abandoned temple not recently visited even by the Sleestak. Will argues with Cha-Ka to forfeit the egg and find another, but it begins to hatch before their eyes. Out pops a baby dinosaur, which Will dubs "junior", and before you know it the mood turns sappy, complete with corny baby music. Junior squawks in a baby-toy squeak, while Holly introduces him to the Land of the Lost. Though an enraged, 30-foot-tall allosaurus waits outside, Holly playfully coaxes Junior to come and meet his mother. Just then Cha-Ka throws an intact end of the egg shell over his head and makes a run for it back to his tribe. Since angry Alice is preoccupied watching Junior, she belatedly chases after the Paku. Will calls out to Big Alice, winning back her attention; both he and Holly manage to flee into the jungle when the mother dinosaur returns to see her newly hatched child.

Ta and Sa run into Cha-Ka on his way back with the egg shell. Cha-Ka explains to Ta that the egg shell is his ("aboba echichi me", translated "allosaurus egg mine"). Ta considers the egg shell unacceptable, wipes off the symbolic white paint streak from Cha-Ka's forehead, and tells the young Paku that he is not a "man". As the older two Pakuni leave behind their rejected clan member, Sa looks back with an apologetic expression. Will and Holly pass by Ta and Sa, receiving no reply to their greeting as they arrive to regroup with their young Pakuni friend. Cha-Ka explains how Ta took away his manhood beads, giving him a "failing grade" on his test; Will speculates that Ta just didn't realize that Cha-Ka's egg hatched. Just then Big Alice's roar can be heard, followed by Ta and Sa fleeing by in terror, but the menace ends up just being Junior. Ta steps out from behind a tree, claiming that he is not afraid, and refuses to believe Will's explanation that Junior hatched from Cha-Ka's egg. Will realizes that since they saw Ta frightened of Junior while Cha-Ka stood by calmly, Ta is reluctant to admit to Cha-Ka's superior bravery and rightly hand over the beads. Cha-Ka gestures to Ta that the egg belongs to him, but the older Pakuni still refuses, shaking his head. Will gets an idea and asks Holly to entice Junior over to them; as the baby allosaur starts coming closer, and with Will blocking a rear escape, under the pressure Ta removes the beads from his neck, places them on Cha-Ka, and hastily dubs the youngest Paku a "man". Ta and Sa scurry away humbly as Will congratulates Cha-Ka. For a moment, Holly is concerned about what to do with Junior, but his mother soon arrives (though still at a safe distance) which takes him off their hands. Cha-Ka then excitedly dabs some of the manhood paint on Will's forehead; Holly jokingly notes that while Cha-Ka has become a man, her brother has just become a monkey! Will mentions the map he needs to finish, so the three all frolic home as corny "Junior" music brings the show to a close.