By the time I started reading Blue Lightning, I was engaged in the story of Jimmy Perez and Fran Hunter - that was what kept me reading the books, that was what I was invested in. The Shetland books themselves, are at times frustratingly slow, and this one suffers from that (Raven Black is the best of the books for pacing). You get so little for so long, then Jane dies, then again little happens.
The thing that kept my attention was the character interaction and the differing views on Jimmy - the impact of a murder happening when he's home and meant to be celebrating. This is all overshadowing by a weak, rushed ending.
Ultimately, I expected the ending - the chosen narrative track for the 'shetland quartet' is Jimmy Perez meets Fran Hunter - falls in love - commits - then loses her. It doesn't work for me. In fact, it's the most frustrating part of reading the books, getting invested, hoping that they wouldn't fall to the trope, then having it do it. Fran Hunter, to use comic book born phrasing, gets fridged at the end of Blue Lightning. Her death does not serve the narrative. It doesn't add anything. All it does is inspire Jimmy's man pain. There is little I dislike more than the woman dying to inspire change and heart ache in their man.
In all but Red Bones - there is a threat play in the narrative in regards to Fran - she could be next, but isn't. You get to Blue Lightning, and besides her presence on the island, and connection to Perez, there is no reason to suspect she will die, apart from the constant foreshadowing in the previous books.
Add in the fact that Jane and Fran are both killed for playing detective - and when there are others who could have acted to save them - is annoying, because it plays into the kind of anti-active women tropes that exist far too much. Why couldn't the trope have been turned and Fran have presented the answer? Why couldn't poor Sarah get some strength in the end?
Fran could have actually been an active partner for the first time in the books, instead of Perez's fantasy. Or if you wanted to explore real tragedy, given the thing about a baby, Fran could have survived but with consequences.
So much is raised but not dealt with in this story - much of it relating to women and their power over their lives - ultimately, Jimmy and Fowler are the ones with the power (and Big James) while the women get to be the passive participants in the story. Fowler kills Fran as a last power play effectively. The last twenty pages of the book suddenly throw together something resembling an ending, that isn't satisfying, and lacks the charm of the previous books.
I will be reading Dead Water at some point - but my interest in Jimmy Perez's story has faded, with the key driving relationship dead.