Peri and Frobisher are rummaging through a storage room in the TARDIS. Peri is so taken aback by the cultural treasures she discovers that she doesn't pay attention when the Sixth Doctor reports that there is an intruder aboard the TARDIS. Peri and Frobisher decide to explore the TARDIS some more, while the Doctor investigates the intruder. The Doctor discovers a Swuffle he brought aboard was in fact a shapeshifter, a Kymbra Chimera. The shifter changes to the form of Peri, but Frobisher quickly spots the difference: Peri's clothes and necklace are fused into "her" flesh, as the Chimera is unable to duplicate clothing. The Chimera and Frobisher fight as the Doctor discovers a way to suck the intruder out the TARDIS. He does so in the nick of time.