Black Orchid was the fifth story in season nineteen of Doctor Classic which has precious little going for it and felt like a stretch, even at only two episodes long, with no aliens or monsters or anything else science-fictiony other than them showing in the TARDIS to liven things up - WTF?
Some fans may like it because it's a historical, even though much of the portrayed "history" was bollocks. Fans of Downton Abbey might like it too I guess, considering the setting; they'll watch anything from the Beeb with period dress. It appears to have been the Fifth Doctor's highest-rated story, so maybe this marks the point when things really began to slide. It starred Doctor Fivey, Nyssa, Tegan and Fucking Adric.
The TARDIS and crew land on 1925's Earth and Davison gets to play cricket because he's been waiting for the chance all this time in that outfit wot. They all go to a fancy costume-dress ball, but someone gets kilt and the bad guy - who's totally not a monstrous alien, cyborg, time traveler, canned brain, returning villain or mutant giant earlouse or something - ends up falling off the roof and dying.