Venus and Earth form as near-twins from the same cloud of gas and dust that built the early solar system, and this episode traces how one became a garden world while the other turned into a furnace. Venus now rotates backward, so slowly that its day is longer than its year, and its surface sits buried under a dense, toxic atmosphere thick enough to crush and cook anything that lands there. The film reads the planet's volcanic terrain as a fossil record of the catastrophe that reshaped it, and lays out the case for a runaway greenhouse effect that boiled away any oceans it may once have held. Scientists interviewed treat Venus as a working laboratory for planetary evolution, using it to test ideas about what makes a world habitable or hostile. The episode also covers proposed exploration hardware: floating bases suspended in the upper atmosphere, designed to lower probes toward the surface in search of physical evidence from Venus's earlier, wetter era.