I've been meaning to read this book by Victorian rural author Honey Brown (and not just because she's another Victorian Rural Woman!) for ages, but the arrival of her second book was a substantial reminder!
From the Blurb:
Shannon and Rohan Scott have retreated to their family's cabin in the Australian bush to escape a virus-ravaged world. After months of isolation, Shannon imagines there's nothing he doesn't know about his older brother, or himself - until a stranger slips under their late night watch and past their loaded guns.