This would have been better as an original novel set in its own universe rather than one set in Star Trek universe.
Capulon IV is about to have its newest King crowned, but his twin brother (thought to have been dead since birth) appears and knocks out and locks up the rightful future ruler so that he may be king. The Enterprise arrives because two nuns, members of the Little Mothers, are to help with "different" children on this world, as well as to sign a treaty with the Federation. Picard, Troi, and one of the nuns are captured and then the book becomes a question of escape, stopping the imposter from getting the crown, and getting a treaty signed.
This is only a Trek novel because of the characters. This would have been a massive budget saving episode had it been filmed because only three sets would have been needed: the temple, the prison, and the throne room. There is nothing science fiction about this story, except for latent telepaths. There's a lot dealing with telepathy in this book, but all that's done with it can be expected early on from the reader. It was tedious with one character continually saying they could help with something, running from helping, and then returning to help. Once is fine, twice establishes a pattern, and the third and fourth, etc., is numbing. The final 26 pages add nothing to the story that the reader hasn't already expected.
This was not a poorly written story, but an unsurprising plot. This was not for me.