When Phil falls through Dr. C's living-room floor while doing aerobics, the scientists suggest using a pulley to extract him, and he is reminded of the last time he saw one in action. . . Ogg was chasing a butterfly--hoping to make it into a sandwich--when he tumbled off a cliff and into a tar pit. Cro's attempt to rescue him seemed doomed to failure by the low-hanging tree branches in which his vine lariat became entangled. But he managed to pull it free of most of them, and Ogg was able to place the loop around himself. Cro, Pakka, Bobb, and Gogg pulled on the other end of the vine, and with the single branch over which it still passed redirecting the force they exerted, lifted him out of the tar.
When Ogg swung back onto solid ground, Pakka congratulated him on "inventing" the pulley, and he became fascinated with the idea. After she and Cro showed him something more of how pulleys work using diagrams and demonstrations, he determined to put one into use himself. His efforts deposited Gogg at the bottom of a deep pit, where he discovered a network of caves prowled by the always-hungry sabertooth Selene.
Ogg, Cro, Pakka, and Bobb built a heavy-duty pulley over the shaft down which Gogg had disappeared and lowered themselves into it. They moved through the echoing depths until they found Gogg, cornered by Selene. An effort to lift a heavy stone, using a jut of rock as a pulley, and swing it into Selene failed when Ogg released the end of the vine too soon, and they were discovered. Fortunately, as they gathered smaller rocks to throw at her they inadvertantly created a chink in a natural dam which formed one end of the cave they were in, releasing a rush of water.
They had just enough time to run back to where they entered the caves and use the waiting pulley and vines to raise Pakka, Gogg, and Bobb to the surface before Selene recovered from her soaking and caught up to them. As a wall of water hurtled toward them, Cro and Ogg tied one end of the vine to a nearby log and the other around themselves. The force of the water carried the log into Selene and then away, and Cro and Ogg were pulled to safety.
Phil's reminiscences come to an end as Dr. C. puts the finishing touches to her block and tackle. She and Mike heave him out of the hole in her living-room floor, but drop him again before they can get him back on secure footing. This time, he falls completely through and lands on the ground floor just in time to open the door to Dr. C.'s dinner date, who runs away screaming.