The fourth Tom Baker/Mary Tamm audio drama from Big Finish Productions, "Phantoms of the Deep," came out in May 2013.
A submarine deep in the Marianas Trench discovers… a blue police box. Inside the TARDIS, the Doctor (Baker) is finishing repairs to K-9. The sub captures the TARDIS, takes the Doctor, Romana (Tamm), and K-9 (John Leeson) on board, then jettisons the TARDIS to the surface.
The sub's commander, Dr. Patricia Sawyer (Alice Krige), says, "Don't worry, Doctor. There's nothing down here that can possibly harm us." (In New Babbage, they know what usually happens after saying something along those lines!)
The group encounters squid - and K-9 deciphers their communication: they're warning the crew to return to the surface, or otherwise they will all die.
Ignoring the warning, they continue through a force field, and hull pressure reduces to almost surface levels. They find a World War II-era submarine, over 100 years old. The Doctor and Dr. Sawyer swim to the WW II sub and discover a survivor, Midshipman Jack Hodges (Gwilym Lee), who thinks he's been there for about 10 days instead of over 100 years. Creatures in the water have been keeping him alive but playing tricks with his mind. The humans can see these creatures but neither the Doctor nor Romana can. Then a giant jellyfish starts to attack the WW II sub.
The explanation for the goings-on is satisfying, though defeating the menace involves even more hocus-pocus than usual. This is an action-packed story and is played for drama more than humor (though humor has its moments as well).