The sail belongs to a small boat, drifting towards you on the evening breeze. As it comes close you struggle to pull yourself aboard and collapse.
Later, after you have caught your breath, you realize the boat has changed direction and gained speed. There is no one else aboard, but it seems purposeful. It seems to have a destination in mind.
For some time you sail on in the gathering darkness until lights appear on the horizon. Soon the boat approaches a small rocky island, and drifts to a stop by a lighted stone pier.
Perhaps now would be a good time to get out .