Blue Lightning by Ann Cleeves

A remote island on lockdown. A killer on the loose . . . Shetland detective Jimmy Perez knows it will be a difficult homecoming when he returns to Fair Isle to introduce his fiancee to his parents. With the autumn storms raging, the island is cut off from the rest of the world. Then a woman's body is discovered at the renowned bird observatory, with feathers threaded through her hair. Perez has no support from the mainland and must investigate the old-fashioned way. He soon realizes that this is no crime of passion - but a murder of cold and calculated intention. There's no way off the island until the storms abate - and so the killer is also trapped, just waiting for the opportunity to strike again.