“The Doctor Trap”
Of all of the Doctor’s foes, Sebastiene is one of the most interesting ever encountered since he is essentially The Doctor’s moral opposite, possessing a personality almost exactly like his rival while being simultaneously completely insane, possessing a significant intellect and capable of great feats but completely disinterested in anything but his own amusement and enjoyment regardless of the costs to others. One of Sebastiene’s main weaknesses is actually his intelligence; he spends so much of his own time over-planning everything that he believes that everything must have a hidden agenda or fallback plan behind the obvious one, The Doctor once commenting that Sebastiene is now almost incapable of believing anyone to be what they claim to be.
Sebastiene’s precise origins are unknown. According to a tale he told Donna Noble – although the accuracy of this is questionable given his own nature – he was originally a Cambridge undergraduate from 1973 who volunteered to investigate a strange meteorite for an experiment, which resulted in a blinding flash that somehow teleported him to Planet 1, the most mysterious planet in the universe, which possessed advanced technology that could essentially reshape the planet’s environment simply by using Sebastiene’s thoughts. Quickly growing bored of his life as a virtually omnipotent entity with no real challenges or goals left to keep him going, Sebastiene eventually began to hunt various life forms from across all of time and space. Eventually reaching a point where he had hunted almost every life form in existence and beaten them all, Sebastiene resolved to target the ultimate prey; the last surviving Time Lord, The Tenth Doctor (Why he targeted this particularincarnation was never specified; presumably Planet 1, like Gallifrey and the Guardians, operate along a single fixed timeline even for time travellers such as The Doctor, with The Tenth Doctor being The Doctor who existed at ‘present’ from the planet’s perspective).
To this end, Sebastiene contacted the Society of Endangered Dangerous Species – the name omitting the fact that the Society were often the people who had made the species in question endangered in the first place – offering them the opportunity to hunt the last Time Lord after luring The Doctor into a trap. In an attempt to better predict what The Doctor would do, Sebastiene even hired The Doctor’s ‘number one fan’ – a young man called Baris who had spent his life ‘wired in’ to telepathic computers that told him every known fact about The Doctor – and had him surgically altered to look like The Doctor, offering to allow him the opportunity to replace The Doctor by ‘giving’ him the TARDIS and Donna for his own.
Unfortunately for Sebastiene, he failed to understand Baris’s mentality, never realising that Baris would not want to kill his hero simply because Sebastiene would have desired to do so in his place, giving Baris a unique chance to save The Doctor. When Baris was sent to confront and ‘recruit’ The Doctor for the hunt, he deliberately spent a great deal of time telling The Doctor all about Sebastiene’s plan, giving The Doctor enough time to reprogram the teleporter to send the apparently villainous Baris – Baris knew that The Doctor would never have sent him into danger unless certain that Baris was a genuine enemy – into the hunt in his place, simultaneously hypnotising Baris to think that he genuinely was The Doctor (Along with a hypnotic loop that would cause Baris to focus on finding the kidnapped Donna if his real personality tried to assert itself).
The Doctor subsequently teleported back to the main complex of Planet 1 while posing as Baris to try and recover Donna and the TARDIS – Donna having been left in a hotel created by Planet 1 while the hunt took place – also manipulating events in the hunts to ensure Baris’s own continued survival. Even when Sebastiene realised that The Doctor was manipulating events from inside his complex, he simply concluded that The Doctor was actually a brainwashed Baris who was acting as The Doctor’s agent, his belief in developing contingency plans for even his contingency plans preventing Sebastiene from taking anything at face value even when The Doctor admitted his true identity. Taking advantage of this misconception, The Doctor was able to keep Sebastiene occupied by claiming that The Doctor’s death would activate the ‘Doctor Trap’ – without actually saying what The Doctor Trap would do – leaving Sebastiene attempting to question Donna before sending The Doctor – still believing him to be Baris – to try and question her about The Doctor Trap.
Now reunited with Donna – subsequently finding Baris and breaking his conditioning – The Doctor realised that someone else had been helping him in his attempts to keep Baris alive, as various overrides had been left in the computer for him to use. Tracking the members of the Society of Endangered Dangerous Species to the zone where he and Donna had first arrived on Planet 1, The Doctor was able to trick them into defeating each other by unleashing a beast that had been hiding in the zone before confronting Sebastiene. Using Sebastiene’s constant need to find hidden agendas in everything, The Doctor informed Sebastiene that he was actually a robot created by Planet 1 that thought he was Sebastiene, simultaneously realising that the true ‘trap’ was actually Planet 1 itself, which wanted The Doctor to eliminate Sebastiene and then take over running it (Much like The Master of the Land of Fiction had wanted the Second and Seventh Doctors to take his place (“The Mind Robber”, “Conundrum”). Refusing to allow the planet to replace him, Sebastiene helped The Doctor and Donna regain the TARDIS and depart, subsequently remaining with Baris to regain control of Planet 1 (Although The Doctor admitted as he and Donna departed that he might have been lying about Sebastiene being a robot, the truth was apparently too complicated).