The Deep is a 2010 Big Finish audio short story read by Peter Davison. It features the Fifth Doctor and Nyssa. It is most notable for being the first piece of Doctor Who fiction written by the award-winning author of young adult fiction, Ally Kennen.
Narratively, it is one of the rare stories that dealt with repairing the chameleon circuit.
When Nyssa attempts to fix the chameleon circuit, the TARDIS turns into a whale. Can she and the Doctor recapture it and turn it back into the old TARDIS before it's stuck in the form of a whale forever?
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- Nyssa is not the only companion to have an idea about how to fix the chameleon circuit. The "Doctor Donna" seemed to have the solution right on the tip of her tongue, right before she had to have her memories wiped by the Tenth Doctor. (TV: Journey's End)
- The Doctor mentions having a TARDIS manual, as seen in The Pirate Planet and Vengeance on Varos, and wonders how Nyssa could possibly have begun repairing the chameleon circuit without it.
- The Doctor is said to have a symbiotic relationship with the TARDIS, as stated in many stories, including Journey's End, The End of the World and others.
- The rhythm of the Doctor's double heartsbeat is used to call the whale-TARDIS under water. It's foleyed to be exactly the same four-beat structure as the Master's heartsbeat in TV: The Sound of Drums.