In chapter 14 of Kidnapped, David is stranded on a small island. He describes this as "the most unhappy part of my adventures" and thinks he is likely to die of cold. He is even afraid to sit down for fear of freezing. Rain and mist come to add to his miseries, and he can find nothing to eat but a few periwinkles.
On the third day, David sees a boat and calls out, but the fishermen ignore him. The next day, he sees the same boat, evidently on its return journey. He runs out to sea and manages to exchange a few words with one of the men, though they do not speak much English and he does not understand Gaelic. He does catch the word "tide," however, with which the man laughs and gestures to the other side of the island.
David rushes to the other side of the island, where he finds that a low tide allows him to wade across to the larger neighboring inhabited island with ease. He concludes:
A sea-bred boy would not have stayed a day on Earraid; which is only what they call a tidal islet, and except in the bottom of the neaps, can be entered and left twice in every twenty-four hours, either dry-shod, or at the most by wading.
The man in the boat, therefore, who is not named, was the one who helped David to escape by telling him about the tides. David ends by saying that he starved with hunger and cold on the island for almost a hundred hours and:
But for the fishers, I might have left my bones there, in pure folly. And even as it was, I had paid for it pretty dear, not only in past sufferings, but in my present case; being clothed like a beggar-man, scarce able to walk, and in great pain of my sore throat.