The Jeremy Brett TV shows he did as Sherlock Holmes are amazing...the best incarnation of any of the Holmes movies or television shows. However, as the years passed, occasionally the show had a few letdowns...and in the final few episodes, there seemed to be more. Part of this is because the producers tried retooling the series but stretching the shows out to double length (a HUGE mistake in hindsight). Another part probably was because Brett was dying and simply didn't have the strength to give it his best. Sad...but he soldiered on. In this case, "The Cardboard Box", Holmes is given very little to do...again, most likely because he was so sick. He was so sick that the previous Sherlock Holmes episode starred Charles Gray as Sherlock's brother, Mycroft...and Mycroft investigated the crime instead of Sherlock in the original stories. Because of this, the final series ended on a bit of a whimper instead of in a blaze of glory.
The story begins with two sisters fighting and you assume the oldest sister is just a nasty twit. Well, don't make any such assumptions! It turns out much of the reason the older one is so angry is that she has reason to suspect her sister Sarah had done her best to break up the third sister's marriage! When the youngest sister disappears, the oldest engages Holmes to find out where she is. Soon after, a police inspector approaches Holmes about a grisly discovery...a woman received a pair of human ears as a Christmas present!! And, perhaps coincidentally, this is the SAME woman who engaged Holmes to find her sister!
The case just gave Holmes very little to do, though it is interesting and worth seeing. Not a strong episode but one that isn't bad at all.