Last night I remembered a pre-DWAITAS Doctor Who plot hooks thread over on RPGnet from 2007 (here) so here are my contributions, including an opening scene I'd completely forgotten about.
Fury Of The Northmen
Setup: Scandinavia, 986 A.D. A Viking war-party makes camp before sailing, and one of the group goes to catch some game for the fire - but a creature with leathery green skin and gleaming yellow eyes hunts him down instead!
The travellers stumble out of the TARDIS into the middle of a dense pine forest. They find a Viking village in uproar. Three of the town's best men disappeared at night, and the others returned to tell of it. Suspicion naturally follows on the strangely-attired travellers, but the warband leader points out that none of them have shining yellow eyes or green skin. Talk of serpents and troll-kin fills the great hall, and a larger warband forms.
Complication: With or apart from the Vikings, the group investigate and find that the area near the camp is slightly radioactive. Following the readings to the source, they find a downed spacecraft being very slowly repaired, humans mining to retrieve metals, and armoured humanoids with green skin guarding them. Ice Warriors!
The Martian soldiers crashed on Earth after a meteor collision, and have been working to repair their craft. So far it can hover, and the tractor beam works, but they need metal to repair the ion engines, and so have taken to grabbing humans. They started with the Vikings' own slaves, but the warriors make stronger miners than the thralls. The Ice Warrior commander intends to release the prisoners once the work is completed, having no interest in keeping humans as pets, but insists that they have to keep them for at least six more weeks at their current numbers.
Action: Between a band of Vikings looking to re-enact the story of Beowulf and a group of Ice Warriors ready to devastate Scandinavia if further threatened, the group have some rather delicate negotiating to do. This could possibly involve access to TARDIS supplies and use of a sonic screwdriver to speed up the mining in exchange for a release of the prisoners.
And as they try to find a peaceful settlement, the imprisoned Viking raiders escape and attack!
Fun Stuff: Vikings! Ice Warriors! Flying longboats! It's like The Thirteenth Warrior crossed with Enemy Mine, a look at two honourable warrior cultures butting heads and refusing to back down. Throw in a commentary on slavery and stir.
The Sleeping Planet
Setup: The TARDIS materialises on a planet with a breathable atmosphere, in the year 31682. Finding a large sanctuary base of the Great And Bounteous Human Empire, the group find that everyone on the base, apart from a group of Ood kitchen staff, is in a coma...
Complication: A being of psychic energy lives on this planet, and appeared to demand that the meat-things leave. When the Empire colonists refuse, not understanding it, it reaches into their minds and puts them all into comas. The Ood, being used to empathic commands for dormancy, remain conscious and do their best to keep everyone from starving to death, but several key maintenance tasks need to be done before the base breaks down entirely.
Action: Then the resident appears before the group and makes the same demand. At least they can understand it. Can the group make peace with it or find another way to wake the Sleeping Planet?
Fun Stuff: Chatty Ood bumbling around in the middle of a base full of unconscious people. Heroic space explorers. A cross-species crew including Draconians and Ice Warriors as well as humans and just-about-humans. A psychic spirit-being making unreasonable demands.
The Midnight Dance
Setup: Following warnings of a temporal flux, The Time Lord and companions find themselves invited to a masquerade ball in Paris, 1890, the invitation handed over by a figure in a mask and top hat who seems to be waiting for them as they step out of the TARDIS. He also provides a blank cheque to the Worth design house for suitable clothing. He basically does more than enough to make sure they'll attend if their basic curiosity at this very strange event and its likely connection to the flux somehow doesn't draw them in.
Complication: While at the boutique, the group are separated, and the masked figure approaches the Time Lord. "My employer knew that you would come. She sees the future as easily as I see you now."
The dapper Fantomas-lookalike works for an oracle, someone who (due to some phlebotnum reason possibly related to the Time War) can predict the near future quite reliably and in particular can sense temporal changes - like the arrival of a time machine.
Meeting the oracle at the ball, the Time Lord finds himself waltzing with a woman who has more in common with him than anyone else he's met since the War. Any romantically-inclined companions are liable to feel a tad jealous.
Action: The masked man steals a TARDIS key while its holder gets changed for the ball. He is a temporal outsider himself, using the oracle to escape from being marooned on earth in the 1890s. A fighty Time Lord or companion can discover this as she sees him dealing with three other figures with scarves concealing their faces.
Unmasked - ideally at midnight, as the bells ring out from Notre Dame as the fight overlooks it - he stands revealed as a near-humanoid alien whose escape would endanger time and space as well as stranding the TARDIS crew.
The oracle pitches in to defeat him, sadly, offering the group some advice on the masked man's actions, and after he is defeated she warns them of some threat in their futures...
Fun Stuff: A companion who likes dressing up having carte blanche in the late 19th Century's leading fashion house, a less keen one having to get dressed up and go to the ball. Carriage chases. Mysterious masked figures with swordcanes. An oracle, who can reveal hints about the Time Lord and companions' futures. Characters who act unsurprised by anything the group does. Jokes about corsets.
A hook involving Tesla as a possible PC, as requested by the OP:
The TARDIS gets pulled in by a spaciotemporal whatchamacallit to 1921, and opening the door the PCs find that it's landed in the middle of a crackling electrical field generated by massive metal coils all around it.
And just outside, a thin, intense-looking man aims a primitive gauss rifle at them with one hand while the other rests on a big Frankenstein lever. (I have snce learned that this is called a "knife switch" but you knew what I meant anyway, right?)
"Aha! I knew there was a time machine in the area. Now. I need your assistance... something has been stolen from me..."
This sets up Tesla as a bit antagonistic right off, but also underscores his super-genius credentials, building a trap for passing time machines just to get one to bring him back a month to when his prototype for something big was stolen (by the thief PC, naturally). And it lets Tesla's player cackle and play with lightning immediately, if they so desire.
The thread also includes Russell Bailey pre-empting The Stolen Earth, Benjamin Baugh setting Nazis against Daleks and Dave Chapman offering a Cybermen plot and saying he really wanted to write a Who game... hmm...