Last One Out by Jane Harper

In a dying town, Ro Crowley waits for her son on the evening of his 21st birthday. But Sam never comes home. His footprints in the dust of three abandoned houses offer the only clue to his final movements. One set in. One set out. Five long years later, Ro returns to Carralon Ridge for the annual memorial of Sam's disappearance. The skeletal community is now an echo of itself, having fractured under the pressure of the coal mine operating on its outskirts. But Ro still wants answers. Only a few people remain. If the truth is to be found in that town, does it lie among them?