An elderly man lies sick in bed, weak and cold, close to death. As he drifts into sleep, something strange happens: instead of dreaming, he wakes into a memory, the first night he spent with his wife. The title, "Time Traveller," fits this neatly. The journey isn't made by machine but by the mind, in the blurry space between sleeping and waking.
The phrase "overtaking the sea in sleep" is the most striking image. It suggests sleep carrying him faster than the tide, perhaps toward death, perhaps backward toward youth. The speaker doesn't sound frightened. He sounds quietly amazed, even grateful, that the oldest and warmest moment of his life is waiting for him.
The mood is tender and bittersweet. The cold, ill body of the opening contrasts with the intimacy of the final line, and the short, plain lines mimic a slow, fading breath. Love, the poem implies, outlasts the body that felt it.