PAOLO SAVERINI'S WIDOW lived alone with her son in a poor little house on the ramparts of Bonifacio. The town, built on a spur of the mountains, in places actually overhanging the sea, looks across a channel bristling with reefs, to the lower shores of Sardinia. At its foot, on the other side and almost completely surrounding it, is the channel that serves as its harbour, cut in the cliff like a gigantic corridor. Through a long circuit between steep walls, the channel brings to the very foot of the first…