The Island by Adrian McKinty. It was supposed to be a family holiday but an accident changed everything. After moving from a small country town to Seattle, Heather Baxter marries Tom, a widowed doctor with a young son and teenage daughter. A working holiday to the Australian outback seems a perfect way to bring the new family together. When they discover a remote Dutch Island, off-limits to outside visitors, the family talks their way onto the ferry, taking a chance on an adventure far from the reach of iPhones and Instagram.
Soon as they set foot on the island, which is run by a tightly knit clan of locals, everything feels wrong. Then a shocking accident propels the Baxters from an unsettling situation into an absolute nightmare.