Sixteen-year-old Odile Ozanne is an awkward, quiet girl, but everyone knows she's destined to land a coveted seat on the Conseil. In her apprenticeship, she competes to become one of the judges to decide who amongst the town's residents may travel across the border. If she earns the position, she'll decree who may be escorted deep into the woods, who may cross the border's barbed wire fence, who may make the arduous trek over the western mountain range—or perhaps the eastern range—to descend into the next valley over. It's the same valley, the same town. However, to the east, the town is twenty years ahead in time. To the west, it's twenty years behind. The towns repeat in an endless sequence across the wilderness. The only border crossings permitted by the Conseil are mourning tours: furtive viewings of the dead in towns where the dead are still alive.

Odile, wise beyond her years, will surely pass the Conseil's vetting. But when she happens upon a mourning tour she wasn't supposed to see, she realizes her dear friend Edme's parents have crossed the border from the east, from twenty years in the future, to view their son still alive in Odile's present. Edme, who's so funny and light. Edme, who's a violin virtuoso at just sixteen. Edme, who's the first boy to even see Odile, to really like her.... And it's Edme who's going to die.

Sworn to secrecy by the Conseil in order to preserve the timeline, Odile finds herself drawn even closer to the doomed boy. When Edme dies far sooner than Odile expects, when she does nothing to thwart his fate, she's deeply shaken. The loss, her foreknowledge, the weight of her rare and varied grief all throw Odile's own future, her adult life, into a devastating, downward spiral.