Deep Blue (novel)

 was the twentieth novel in the BBC Past Doctor Adventures series. It was written by Mark Morris, released 1 March 1999 and featured the Fifth Doctor, Tegan Jovanka and Vislor Turlough.

It also featured UNIT, Brigadier Alistair Gordon Lethbridge-Stewart, Captain Mike Yates and Sergeant John Benton. Also, it sees a character development for Tegan, with her falling in love in this novel.

Publisher's summary
''When a lighthouse keeper reports seeing a ball of light plunging into the sea off Tayborough Sands, UNIT sends Mike Yates to investigate. The last thing he expects to find there is an old friend — with a new face...'' The Doctor and his companions arrive on a pleasure beach in the 1970s, hoping for time off after their latest adventures. But they do not get to relax for long. Violent incidents are at an all time high in the area and people are going missing — or else changing into something more than human...

The Doctor soon realises a sinister presence lurks in the cold seas off Tayborough Sands — a presence with sinister designs on humanity.

Plot
to be added

Characters

 * Fifth Doctor
 * Tegan Jovanka
 * Turlough
 * Brigader Lethbridge-Stewart
 * Captain Mike Yates
 * Sergeant Benton
 * Derek Etkins
 * PC Andy Weathers
 * Tony Maybury
 * Imogen Maybury
 * Charlotte Maybury
 * Chris Maybury

The Doctor

 * The Doctor refers to his third incarnation as "arrogant" and "overbearing".
 * He buys a 99 ice cream with glittering purple shells.

Spacecraft

 * The Xaranti ship is a Morok battle cruiser with some amount of Kraal technology.

Technology

 * The Doctor explains that the TARDIS has an in-built function that allows it to home in on suitable areas for materialisation, which is why it never materialises in solid rock or under water.
 * The Xaranti virus or plague, which they call "Xaranti energy," is psychological: people infected think they're becoming Xaranti, so they physically mutate.

Continuity

 * It's been 6 months since UNIT dealt with the Global Chemicals incident. (TV: The Green Death) with the Third Doctor currently off on his own while Mike Yates is recovering from his brainwashing.
 * The Xaranti warred with the Zygons, destroying their planet. (TV: Terror of the Zygons)
 * The Doctor, Tegan and Turlough are spending a vacation in order to recover from the events of Sea Base Four. (TV: Warriors of the Deep)
 * Turlough is still trying to make amends after working for the Black Guardian. (TV: Mawdryn Undead)
 * Tegan last saw her grandfather just before he was about to move house and had promised to visit him as soon as she returned from Amsterdam (TV: Arc of Infinity) and thinks of asking the Doctor to visit him. (TV: The Awakening)
 * Tegan thinks about staying in the 70s, but even if she did, she couldn't prevent the Master from killing Auntie Vanessa. (TV: Logopolis)
 * Turlough sees cobwebs in the TARDIS but has never seen spiders. Benny will later pass by whistling spiders in the TARDIS. (PROSE: Sky Pirates!)
 * The Doctor uses the IRIS machine again, though reluctantly as the last time he did so someone died. (TV: Planet of the Spiders)
 * The Doctor tells Mike Yates that he has regenerated twice since he last saw him. (TV: Planet of the Spiders, Logopolis)
 * Turlough is worried that he might meet the Brigadier now, but the Brigadier didn't recognise him later when he turns up as a pupil at the school where he teaches Maths. (TV: Mawdryn Undead)
 * Tegan remembers being possessed by the Mara, and implies it's the only time she's been possessed, the Xaranti being the second force to do so. (TV: Kinda, Snakedance, PROSE: Mark of the Medusa)
 * Turlough laments not being given a TARDIS key. (AUDIO: Devil in the Mist, The Kamelion Empire)
 * The Thirteenth Doctor will later encounter another scorpion-like race of scavengers lead by a queen in a stolen spaceship. (TV: Nikola Tesla's Night of Terror)