The would-be highwayman killer's case is closed, and Luis has been cleared to return to work. He and Donovan are starting their new life together, and while they're both a little new at this whole "stable relationship" thing they're determined to make things work. When people start dying at Assonet Ledge, it seems like a typical case for Donovan until one of the victims turns out to be a missing person from out of state, bringing the FBI into one of Donovan's cases yet again. The park ranger at the site is everything Donovan isn't, and Donovan finds himself wondering if his partner isn't falling into old habits. Luis struggles to understand Donovan's jealousy, which puts a strain on their relationship and the case. To top things off, there may be forces at work here that go back long before humans showed their faces, forces Luis can't hope to understand. Will those forces propel the case, and Luis and Donovan's rekindled romance, off a cliff?