The Trial of a Time Lord, Part Eleven (Terror of the Vervoids)

Mel overhears someone plotting to kill all the animal-king onboard the Hyperion and has taped the conversation, unfortunately the tape vanishes. Meanwhile Bruchner is becoming increasingly worried about the situation in the Hydrophics Centre. It is soon discovered that the creatures that emerged from the pods are Vervoids and they are using the ships air ducts to move around unseen.