Standing on a sunny beach, the speaker watches the waves pull back and wonders what the sea will leave on the sand. The mood begins with curiosity and a lightly playful tone, but it shifts as the poem goes on.
The second stanza describes how people notice the tide's steady rhythm and head out to search the wet sand. What they find is a pile of small, odd things: seashells, a lost earring, green glass, branches that look like bones. The speaker calls it "baubles and useless stuff," which sounds a little dismissive, and the bones hint at something darker beneath the pretty day.
The last stanza turns more serious. Even trinkets can cut, and blood is drawn. Then comes the hopeful, slightly unsettling idea that the waves might bring a key to a long-locked door, letting something "forgotten" return. The speaker seems both drawn to and wary of what the sea might hand back, whether that is an object or a buried memory.