One morning, high in the Dolomite mountains, two hikers are some distance apart. The path in places is narrow and perilous. One man falls to his death.

The other sounds the alarm. But these men are not strangers. Members of the same revolutionary group forty years earlier, the first had betrayed the second, who must now hold his own against a young magistrate intent upon having him tried for murder.

Was their meeting an improbable encounter, or an impossible coincidence? Impossible is a brilliant hymn to the lure of the mountains, an engrossing illumination of political brotherhood, and also the subtlest of detective stories.