More people disappear or are killed; the plant pods have been tampered with and the Vervoids—sentient plant creatures—are unleashed. Mel gathers clues via the hydroponics centre; the Doctor uncovers evidence of sabotage among the scientists Bruchner, Doland, and Professor Lasky. Alongside the plant threat, tensions rise among the native species aboard the ship (the Mogarians), and the threat becomes existential: the Vervoids intend to eliminate animal life for their own survival.