Although it's apparently the first Sherlock Holmes story, this is nevertheless a curious choice to start off the TV series, since the story involves a king and a woman whom Sherlock admits "has a face to die for." Purely an observation on Sherlock's part, of course. But it could easily mislead the first-time viewer, as if this new series would involve the titular character in majestic cases with kings, or have love interests. Which wouldn't be too surprising, considering how far from the source material the countless other adaptations before (and since) have strayed.
Luckily, that's not the case. This is a great story, wonderfully produced and a great start. Jeremy Brett and David Burke's performances here are the key; they would either persuade you to give the rest of the series a chance, or dismiss it altogether from the start. Since they are both perfect fits for their parts, everything works.
Holmes is contacted and employed by a king, who fears that a lady from a past relation may want to ruin his upcoming wedding, which could have an impact on European history. This is no ordinary lady, she's very liberal for her time, an opera singer, and very attractive. However, as Holmes finds out soon, she wants nothing to do with the king.
Although the two title performances are always great (and I must also compliment Rosalie Williams as Mrs. Hudson, who is always a joy to see) for me, the main attraction of the Granada series has always been the production values: the sets, costumes, manners of speech and walking, faithfulness to the original material and dialogue, and the general atmosphere of the final work. This episode, like many others, delivers in all these aspects. It's far from being my favorite, but I can always enjoy it when I catch it.