The Secret in Vault 13 (novel)

 a novel released in 2018 by BBC Children's Books. It was written by David Solomons and featured the Thirteenth Doctor, Graham, Yaz and Ryan.

Publisher's summary
A sinister school where graduation means death...

A monstrous mystery lurking below a quiet London street...

A desperate plea for help delivered by... hang on. A potted plant?

The Doctor has been summoned. The galaxy is in terrible danger, and only a Time Lord can save it. But to do so, she must break in to an ancient vault on a remote and frozen world - from which nobody has ever returned alive...

Can the Doctor and her friends Yaz, Ryan and Graham uncover the shocking secret in Vault 13?

Chapter titles

 * 1) Diddly-dum Diddly-dum Woo-woo
 * 2) Bigger on the Inside
 * 3) Re-potted
 * 4) Gardeners' World
 * 5) Non Compost Mentis
 * 6) The Curatrix
 * 7) Gardeners of the Galaxy
 * 8) Cuppa Tea?
 * 9) The Last Guardians
 * 10) Dorm
 * 11) Please, Miss, I Feel Sick
 * 12) The Faculty
 * 13) Always Keep the Warranty
 * 14) School's Out
 * 15) Exterminate
 * 16) Fantastic Voyage
 * 17) Party Animal
 * 18) Unearthly Child's Play
 * 19) By-laws
 * 20) A Hiccup in Time
 * 21) Kensington Gore
 * 22) Run!
 * 23) We Belong Together
 * 24) The Crack of Doom
 * 25) Breaking Bud
 * 26) An Apple a Day
 * 27) Plants Within Plants
 * 28) Sunset
 * 29) What Would Werelock Do?
 * 30) Always Remember to Back Up

Plot
The Fleet was planning an assault on the Avolantis System when the Thirteenth Doctor, Graham O'Brien, Ryan Sinclair and Yasmin Khan visited their planet. Space Lord Draal took possession of the TARDIS and sent a Mark VI combat mechanical to capture the crew. The Doctor reprogrammed this and other Mark VIs to prevent the Fleet from raging further wars and took prisoners held in Draal's throne room to their homes.

Characters

 * Thirteenth Doctor
 * Graham O'Brien
 * Yasmin Khan
 * Ryan Sinclair
 * Begonia
 * Deadly Nightshade
 * Aisha
 * TARDIS Ryan

The Fleet planet

 * Space Lord Draal
 * Bernard
 * Hydran prisoner
 * Dalse prisoner
 * Chentan prisoner
 * Zraryx prisoner

Tellus IV

 * Willow
 * Parsley
 * Lily of the Valley
 * Oak

Calufrax Major

 * Curatrix
 * The Attendant

New Phaeton

 * Aaron
 * Lalitha
 * Porter
 * Peyton
 * The Faculty
 * M8-Tron

London

 * Tom Manners
 * Mr Delgado
 * Jonathan
 * Jonathan's sister
 * Professor Tarkovsky

Individuals

 * Harry Houdini was known for impossible escapes.
 * Space Lord Draal had the hull of a captured Frost Pirate warship and fins of megalovore sharks, which used to inhabit the Outland Sea, in his throne room.

Species

 * The Fleet conquered 10,000 star systems.
 * Time Lords have two hearts.
 * The Doctor previously defeated Sontarans, Cybermen and Daleks.
 * The Thirteenth Doctor encountered carnivorous chessmen on Proxima Ceti earlier.
 * The Space Lord holds a Chentan, a Dalse, a Hydran and two Zraryx prisoners in his throne room.
 * Giant spiders from Metebelis III have twelve eyes.
 * Gardeners of Tellus IV care about plants.

Animals

 * Bugbeasts of Zeta Draconis are easy to defeat.

Robots

 * Mark VI combat mechanicals are military robots created by the Fleet.

Groups and organisations

 * Frost Pirates were conquered by the Fleet.

Planets

 * The Fleet operates from an unnamed planet.
 * Bugbeasts live on Zeta Draconis.
 * Time Lords from Gallifrey are known to the Fleet.
 * Daleks are from Skaro.
 * Carnivorous chessmen live on Proxima Ceti.
 * The Fleet defeated Murgon III.
 * Hydrans originate from Polaris Alpha.
 * The TARDIS team decides to go to Lotos B but never gets there.
 * The Doctor recalls an orchid seemingly trying to speak to her on Solaria.
 * The TARDIS crew goes to Tellus IV to meet with the Gardeners.

Earth locations

 * Ryan saw the Doctor escape 200 cyborg clones of Houdini in the subways of New York City in 1904.

Other locations

 * Bernard pursues the Doctor, Graham, Ryan and Yaz through the Forest of Desolation, across the Burning Grounds and into the Valley of Agonies.
 * The Citadel is in the Blasted Plains.
 * The Fleet is planning to attack the Avolantis System.

Events

 * The Outland Sea boiled away during the Ice Cap Wars.

TARDIS

 * TARDIS is powered by the Eye of Harmony.
 * TARDIS has two "hearts": the engine room and the circular console room with the console.

Materials

 * Mark VIs were made of phlebotinum.
 * Ryan's clothes is made from cellulose-based materials. His shoes are made from rubber and plastic.
 * The Citadel was made of iridanium steel.

Technology

 * Yaz witnessed the Doctor defusing a temporal anomaly bomb on a derelict space station.

Continuity

 * The Thirteenth Doctor explains that the TARDIS is supposed to blend in with the environment using the chameleon circuit, but it got stuck in a form of a police box circa 1963. (TV: An Unearthly Child, Boom Town)
 * Graham O'Brien was most keen to leave Earth and travel with the Doctor. (TV: Arachnids in the UK)
 * Graham, Ryan and Yaz chose to leave Earth with the Doctor a few weeks ago. (TV: Arachnids in the UK)
 * Graham would not want to run into Ravenous monsters. Incidentally, Ravenous are especially feared by Time Lords. (AUDIO: Seizure)
 * The Doctor recalls how she and Sarah Jane Smith had problems with Krynoids. (TV: The Seeds of Doom)
 * Graham finds a tourist prospect for the Leisure Hive on Argolis, but the Doctor has already been there and had issues with the tachyon generator. (TV: The Leisure Hive)
 * Yasmin Khan never met Graham until their encounter with Tzim-Sha. (TV: The Woman Who Fell to Earth)
 * The Doctor recalls her encounters with Yeti robots. (TV: The Abominable Snowmen, The Web of Fear)
 * They return to water Graham's houseplants a few weeks after first leaving the planet. (TV: The Woman Who Fell to Earth)