to be added
- The Doctor has encountered the skull and crossbones insignia before on Earth, but does not immediately recall its meaning. He wonders if the pirates are from Earth or visited it.
- The TARDIS key is described as an "electronic key."
- The pirates have gills on the back of their necks, though the Doctor doesn't know if this is through evolution or surgery.
- The planet has a red shore with conical mountains beyond.
- This story was included as a bonus story in the 2019 audiobook version of Doctor Who and the Invasion from Space, read by Peter Purves.
- The Doctor recalls the fishmen of Kandalinga. (PROSE: The Fishmen of Kandalinga)
- The TARDIS has a force field. (TV: The Horns of Nimon)