There are a number of reasons why Black Orchid is one of the worst Dr Who stories and easily the weakest BBC Dr Who title to date. Firstly, there's no reason for the Doctor to be in it at all. Aside from playing a bit of cricket, getting stuck in a secret passage, finding a couple of bodies and being suspected of being the killer for about the 100th time before the plot - a tired 20s country house number with under-developed gothic undertones - quickly resolves itself while he's not even around, he has no real impact on the plot (what little there is) and there's no real science fiction or even historical aspect to the story. It's simply an exceptionally weak and very tedious country house non-mystery that plays like an outline for an episode of Ripping Yarns played straight. Worse, it's so uneventful. Even at 49 minutes over two episodes it's mostly filler: in the first episode there's a lot of not very much to set up the not very much that happens in episode two. The direction is dull, the writing mechanical and perhaps the only unique thing about the story is that it shows that the normally relentlessly vile and whingeing Tegan could be nice for an entire story and it wouldn't kill her.
It's not the worst of the stories produced under John Nathan Turner's contentious stewardship, but it's possibly the dullest and most utterly pointless: hard to disagree with the audio commentary on this extracting-the-urine-releasing-this-as-a-single-DVD (on video it was doubled with The Visitation) where the cast basically spend 50 minutes rubbishing its many weaknesses. Extras are pretty thin too - 4 deleted scenes and trims, featurettes on the locations and the Peter Davison Dr Who comic strips, extract from Blue Peter and Points of View, continuity announcements and the usual trivia track and stills montage.