This extremely good story is shamelessly slaughtered.
The plot is spoilt from the very beginning : the first scene shows a man handling a snake and pushing it through a ventilator while another man waits smoking a cigar, and then a girl (Julia Stoner) waking up to find a snake on her and screaming. This spoils all the story : we already know how the girl was killed, and as soon as we see her father and his servant we recognize them and therefore know who killed her.
(NB: I hesitated to check the spoiler box, but how can something be considered a spoiler when it is given away in the first few minutes of the episode ?)
The excellent scene from the book in which Holmes and Watson examine the room, and Holmes ominously points out the coincidences ("A ventilator is made, a cord is hung, and a lady who sleeps in the bed dies. Does not that strike you?") is reduced to a statement by Watson that Holmes has already examined the room in detail a reply by Holmes that now he knows how the girl died. And that is it. To be fair, they already spoiled the plot by showing us how it was done so there is no need to give clues to the viewers, but they did not even bother to explain Holmes' observations and deductions, neither during that scene nor afterwards. It is especially sad when considering that Doyle was always fair : in his stories the deductions make sense, and are based on observations which are pointed out to the reader (unlike most stories where they are hidden until they are to be dramatically pulled out of a hat, or sometimes even things there was no way for the reader to know or even suspect).
Plenty of elements necessary for,the atmosphere of the story are also missing. Nothing at all is said about the character of the father (who has is name changed from Dr Roylott to Count I don't remember what). Nothing about his being a doctor. Nothing about the dismal life both sisters had to live. Nothing about the marriages, probably to simplify the plot. The exotic animals supposed to roam the place freely are replaced by a savage dog, and the exotic animals themselves are mentioned only once as something the doctor/count was once interested in.
As for the acting, I usually don't have anything to say in that regard unless someone strikes me as being extremely good, or extremely bad, which happens very rarely. I don't claim to be an authority on the subject or even to be a good judge of good vs bad acting. However, I was very disappointed by Helen Stoner. She always maintained a wooden expression, slightly puzzled, but she never seems genuinely frightened even when she was supposed to be, nor grieved when speaking of her sister's death. Her lack of expression was rather shocking.
One unclear point in the adaptation can arguably be seen as an improvement depending how you understand it. There is no mention at all of Helen being forced to sleep in her dead sister's room, therefore it is not clear whether the room is the same as her sister's like in the book or another, and whether the ventilator used by the snake communicated with her father's room or outside. After viewing the episode I had the impression that the rooms were separate, and that the father was using ventilators already existing. But I may be mistaken, and I did not have the heart to inflict myself another viewing of this pitiful adaptation.
So, to conclude. You can't watch the episode to find out the answer to the locked-room mystery because the answer is given away in the first scene. You CAN watch it out of curiosity, wondering how Holmes will figure it out, but you will be disappointed because that is never mentioned. You can watch it because you liked the original story, but you will also probably disappointed with so much omissions that only the bare minimum is left. And so much unnecessary additions...
I really don't recommend it. The other, earlier version of The Speckled Band made by Sheldon Reynolds and starring Ronald Howard was much better.
