Dead Letter Days by Kelley Armstrong

Eric Dalton spent most of his life in Rockton, a hidden town in the Yukon for people who need to disappear. Now that sanctuary is gone, and he’s holed up in a wilderness lodge with his girlfriend, Casey Duncan, and their friends, as they scout for a place to build their own Rockton. When Eric and Casey find a literal message-in-a-bottle, it leads them to the mystery of a woman who went missing decades ago, having never received that vital message. As they investigate that cold case, Dalton must finally lay to rest the ghosts of his own past and make some overdue decisions before he’s ready to step forward in his new life with Casey.

Note: This is not a full-length novel. It’s a novella set between the end of the Rockton series and the beginning of the Haven’s Rock spinoff