Roots: Cluedo ('Professor Latterthwaite, in the armoury, with the revolver"), Butterfly effect, Edge of Darkness (Ian MacNeice playing a character named Harcourt) The Doctor paraphrases Dr Johnson's Essay on Tea (1757) (the full quotation is: "Tea's proper use is to amuse the idle, and relax the studious, and dilute the full meals of those who cannot use exercise, and will not use abstinence.") The Dr misquotes Hamlet II (ii), adding "when the wind is in the east" When the Boat Comes In. Fisherman's Friend lozenges.

Technobabble: Among the TARDIS' functions are Osmotic Dampeners, Accelerometers and the Gravitic Drift Compensator.

Dialogue Triumphs: "What did he say?" "-He said 'woof'; he's a dog!"

and, "I didn't understand a yap of that."

How does it feel not being the cleverest man in the room?' 'I wouldn't know. How does it feel?'

"He has the eyes of a killer" "As well as the gun"

"The problem with data is integrity, and you don't know you've lost that until your worlds come crashing down"

Continuity: The Morivanian Museum on Morivania Minor is the greatest collection of Earth artefacts in the known universe. Its wing specialises in Eighteenth and nineteenth century artefacts. Its Renaissance Section was meant to usher in a new era of learning, assimilating knowledge of all experts, but instead it absorbs them through an osmotic process. Among the works and artefacts present the Doctor names works of Holst, Elgar, Butterworth, Lloyd George, Arthur Conan Doyle, Winston Churchill, the King (George V?), Rudyard Kipling, George Bernard Shaw, "thousands of Smiths", Little Titch, Vesta Tilley and Henrik Ibsen. Artists named include Edward Johnson, Miles Kensington Nord, Frederick Leighton, and another named Armstrong ("the texture's unmistakeable")

Professor Hilda Lutterthwaite is a world-renowned lepidopterist ("the lepidopterist.") The artist Millicent Mary Lighthorne was born in Cork and specialised in watercolours, celebrated for her use of light. Her works include When the Boats come in, and The Fisherman's friend. She died of consumption. Dr Henry Carnforth was the author of Mediaeval Builders: the complete and scholarly guide, a definitive text with small print but "terribly good pictures" according to the Doctor.

Leela is a peerless tracker, and the Doctor says she could get them through and back the laborious labyrinths of the Maze-masters of Maprazo

The Doctor hasn't experienced toothache "with these teeth" before (see: Links). His mental defences kick in as his memories come under attack. He is often asked to say a few words at gallery openings on Morivania Minor, and says he used to get on terribly well with dogs. Among his academic acquaintances are Professor Dolorous, and Matthias Pendleton, who "loves a ginger snap." He recalls the Orion Renaissance ("oh, those were the days!")

Untelevised Adventures: The Doctor recalls meeting the Archimandrite of Fastidious Nine

Links: Pescatons. Leela mentions Horda, the Tesh and Xoanon (The Face of Evil) The Celestial Toymaker/The Gunfighters (the Doctor's toothache) Leela says she once fired a pistol at a dragon (The Talons of Weng-Chiang)

Qv: 'Telepathy and ESP'

The Bottom Line: "I probably need to reverse the polarity - that's usually the way it works."

That's more like it! Genuinely funny, inventive and imaginative, with a perfect length and a great cast. There's not much more to add, except to say that this is probably the most enjoyably quotable stories of the Fourth Doctor's first audio season, if not all of 2012.