So Far Gone by Jess Walter

Retired journalist Rhys Kinnick has lived off-grid in a cabin for the past seven years. With no cell phone and not much human contact, he is unprepared when his two grandchildren, Leah and Asher, show up on his front porch. Their mother Bethany, who is Rhys' daughter, left them with instructions to be taken to Rhys rather than left with her husband, Shane. While Shane is a good man, he is part of a group with extremist beliefs that are antigovernmental and religious. So Far Gone is the story of Rhys trying to protect his grandchildren from the people that Shane is associated with. It is also a tale of a father and daughter trying to heal and find their way back to each other. While the plot of the novel sounds grim, Walter infuses it with humor and vivid characters.