Peri Brown's TARDIS key

Peri Brown held possession of a TARDIS key which was given to her by the Fifth Doctor. (PROSE: Fascination)

Peri still had it when she was travelling with the Sixth Doctor. (PROSE: House) She gave it to Janine Foster, who handed it to Kathy Chambers so she could get into the TARDIS if she and Peri were unable to stop the partially-converted Anthony Chambers. (AUDIO: The Reaping)