Third in the Twins of Petaybee series by Anne McCaffrey...
This one and the previous book in the series read like one longer book to me. Of course I read them back to back which encouraged that impression, but the action and plot and all of that pick up exactly where the second book left off.
This one reminded me a lot of the first Petaybee series (which I have read, but not since I started the book blog so no linkies) with the planet itself fighting back. More of a guerilla fight against the authorities kind of feel.
So, all of our good guys are imprisoned or unable to get past communication problems and in desperate need of getting the word out as to what is going on so that the situation can be dealt with. The Big Bad from the first book has reappeared and has one of the twins. I'm not going to give the whole thing away, but there is resolution by the end of the book so no cliff-hanger on this one!
I'm very much hoping that there'll be more books either in this series or in the original Petaybee series. She creates such interesting people and places and I always want more. The idea of a sentient planet is just fascinating (as are selkies!) It makes for such a different world (in the sense of the world of the book, not the planet) when there's this huge entity that is both residence and protector.