Roots: The Red Dwarf episode 'Justice' and the story of Spring-Heeled Jack. Taxi Driver (washing scum off the streets?), Superman ("in his other persona he's simply done his hair differently and put on some spectacles; hardly the most impenetrable of disguises."). Sherlock Holmes' dictum ('When you have eliminated the impossible whatever remains, however sensational, must be the truth.') the catholic prayer of confession ('mea culpa mea culpa, mea maxima culpa"). The Doctor mentions Bertrand Russell, Margot Fontayne and Aldous Huxley.
Technobabble: Ion engines leave a distinct trace which dissipates after a few days
Dialogue Triumphs: 'Who needs intellectual rigour and wisdom when a thoughtful fist can express a thought so eloquently?'
"Is it you-?" "Well, I'm me, certainly. I know that for a fact."
"Either somebody's ordered a Babycham or we've just been rumbled."
"I can see as a group you're rather starved of allure."
"Same muffin man! Where's his career plan?"
"The housekeeper kept offering me food, though for the life of me didn't seem to think I needed cutlery."
"I tell you, it's so frustrating. Time Lords- we can stave off death, perform calculation beyond the ability of most sentient species, travel to any point in history, and yet a length of rope around our wrists and we're about as useless as... well, you."
Continuity: The steam-powered robot Justician comes from the Jalxar Peninsula, a heavily-regulated but peaceful territory. It is programmed to uphold the laws of whatever planet it is located on and needs a local symbiote to provide it with a contextual undersanding of local justice. All serious crimes are punishable by death without recourse to a judge or jury. The Justician is also equipped with a proximity detector and brain-scanning technology. It searches the mind for guilt and pronounces judgement based on what it finds- its subject therefore incriminates themselves. Its cabbie symbiote's equipment comprises body armour, electroshock weaponry and motorised skates.
Ten years have passed since the [Fourth] Doctor last met Jago and Litefoot; Henry is now with the New Regency Theatre, and George presumably still has the same housekeeper.
The Doctor is wearing same deerstalker (and presumably Inverness cape) as in The Talons of Weng-Chiang. His sonic screwdriver works better on steam-driven machinery than electronic. He has with him a five pound note. He states his age as seven hundred and sixty ("good skin, see? Beetroot - takes years off you!").
Links: The Talons of Weng-Chiang. The Doctor mentions K9 (but not by name) and Leela is discussed ("otherwise engaged" is a rather naughty line given Jago's response). The Doctor and Romana detected a damaged alien craft entering earth's atmosphere some three and a half weeks ago (presumably via the Doctor's etheric field disturbance detector).
The Bottom Line: "I dare say we shall meet again, in the fullness of time!"
Witty and derivative without overstaying its welcome. Oddly, not quite as good as Jago & Litefoot's adventures with the Sixth Doctor, but the presence of Romana makes up for that, and everyone is giving it their best regardless- a very welcome reunion.