returning to the desert, dave and arthur trace the fragments to the crashed meteor. arthur deduces that the meteorite's atomic structure has been radically altered by the intense heat of atmospheric friction. back in the lab, a rainstorm blows up while dave and arthur continue their investigation. a piece of black rock falls into the sink and begins to react when hot coffee is poured on it; the men then realize that water is the culprit. with it raining outside, they hurriedly return to the desert and see the black fragments now growing into stories-tall monoliths that rise up and then crash back to earth, breaking into hundreds more fragments, each fragment then repeating that cycle. dave quickly realizes that the monoliths' advancing path will take them directly through san angelo, and from there the monoliths could spread and possibly threaten all life on earth.