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 home planets.

By request of slightly homesick Graham, Team TARDIS returned to Sheffield to water plants in his and Ryan's apartment. One of the plants, a begonia that Graham took with him into the TARDIS used the TARDIS telepathic circuits to relay a message for the Doctor that the Gardeners of Tellus IV need her help.

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.

Species

 * The Fleet conquered 10,000 star systems. The Fleet were governed by the First Space Lord of the Admiralty.
 * Time Lords have two hearts. They have long lives and can create a new body via a regeneration.
 * The Doctor previously defeated Sontarans, Cybermen and Daleks.
 * The Thirteenth Doctor encountered carnivorous chessmen on Proxima Ceti earlier.
 * Hydrans have three heads.
 * Giant spiders from Metebelis III have twelve eyes.
 * In addition to the Hydran, the Space Lord holds a Dalse, a Chentan and two Zraryx prisoners in his throne room.
 * Gardeners of Tellus IV care about plants.

Animals

 * Bugbeasts of Zeta Draconis are easy to defeat.
 * Megalovore sharks used to live in the Outland Sea.
 * Devil Bird was a creature from the Fleet home world.
 * There were sheep on Tellus IV.

Plants

 * Graham has a yucca as a houseplant.
 * Graham takes a begonia into the TARDIS.
 * An orchid seemed to try to speak to the Doctor once on Solaria.
 * Gardeners grow tomatos on Tellus IV.
 * The Doctor asks the Gardeners to take her to their cedar.
 * At Willow's picnic, the travellers sample rainbow-coloured grapes, figs that happily sigh when bitten and blushing strawberries that pulsed in the hand.

Robots

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

Groups and organisations

 * Frost Pirates were conquered by the Fleet.
 * Yaz was well trained by the Hallamshire force.

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 devastated their own home world.
 * Hydrans originate from Polaris Alpha.
 * The Fleet defeated Murgon III.
 * Metebelis III is a planet of giant spiders.
 * 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.
 * Gardeners brought topsoil from their home world.

Earth locations

 * Ryan saw the Doctor escape 200 cyborg clones of Houdini in the subways of New York City in 1904.
 * Graham tells his neighbour that he plans to visit relatives in Australia.

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

Events

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

TARDIS

 * A TARDIS has two "hearts": the engine room powered by the Eye of Harmony and the circular console room with the console. The TARDIS's main door was set in one of the walls of the console room.
 * The Doctor's TARDIS is an old Type Forty.

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.

Earth technology

 * Ryan once rode in a Mercedes with AIRMATIC suspension.

Science

 * Planck's quantum of action is one of the universal constants.

Cultural references

 * Star Trek features the so-called "Prime Directive" not to meddle in other civilisations.
 * Graham mistakes the high-pitched voice of his begonia for the music of the Bee Gees.
 * The Doctor explains the harmlessness of the begonia by saying it is not a triffid.

Food

 * Graham is worried about dropping spaghetti bolognaise on his jumper.

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 Graham's house to water his houseplants, a few weeks after first leaving the planet. (TV: The Woman Who Fell to Earth)
 * The Doctor mentioned that she originally borrowed the TARDIS. (TV: The Name of the Doctor, AUDIO: The Beginning)