Thunder is rumbling over a mill-pond, a man's bare feet are in the water, and a girl in white tells him to be careful. That is nearly all that happens in Edward Thomas's poem, yet it is written as though the moment never ended. The speaker remembers being startled and annoyed by the girl, and "angry till / She passed from sight." The final stanza overturns that irritation. As the storm breaks, she seems "beautiful and kind, too," and the last line insists that she still does. The poem is about how memory revalues the past. A minor irritation hardens into a lasting tenderness, and the speaker understands it only from a long way off.
The opening stanzas build the scene through sound, and the order of the sounds is deliberate. The thunder arrives first as a "boom," then shrinks: it sounds "less than the cooing in the alder / Isles of the pool," drowned by the "plunge / Of waters cool." Then the starlings "outchatter" both the stream and "the next roar / Far on the hill." Thomas's coined verb is comic and exact, since the loudest thing in the landscape is being outdone by small, fussing birds. The storm hangs in the background, never quite taking over, and the effect is of a mind absorbed in nearby detail while something larger approaches. Even the adjectives work this way. The water is "cool," the mill "black," the sun "blazed," so heat, darkness and coolness all press into a few lines.
Light and dark carry much of the poem's feeling. The wagtail "flickered bright over / The mill-pond's gloom," a small flash against a dark surface. When the girl appears, "dressed all in white," she repeats that pattern at human scale, a brightness set against the black mill. The poem never says the two are linked, but the echo suggests that she registers like a sudden flicker, something glimpsed rather than understood. She is also all surface: we get her white dress and her three words, and nothing of her face or name. That thinness makes her easier to reshape later.
The form is simple. Each stanza is a quatrain of alternating longer and shorter lines, and only the second and fourth lines rhyme: gloom/pool/cool, mill/hill, below/ago, white/sight, how/now. Because the first and third lines go unrhymed, the poem sounds like speech more than song. Sentences also spill over the line-endings ("the thunder yet / Added a boom"), which keeps the voice casual and unhurried. Against that looseness, the rhymes that do land are often time-words. "Ago" closes the fourth stanza and "now" closes the sixth, and in between "Ages ago" is repeated almost like a catch in the throat. The first time it breaks into the sentence after a dash, and the past tense we have been reading in suddenly turns out to be a distant one. By the end the long gap has narrowed to a single syllable, "now," as the rhyme with "how" pulls the two ends of the speaker's life together.
"Take care!" is the poem's quiet hinge. On the surface it is a warning to someone with his feet in a mill-race. The speaker took it as an intrusion, which is why he bristles. The storm then bursts and he has to crouch for shelter, and her caution begins to look like good sense, even concern. Whether the phrase carries a wider meaning is left to the reader, but it is hard not to hear the ordinary kindness inside it. Notice, too, that the speaker says she "seemed" beautiful. The verb admits that this is how memory and affection have made her, not a fact he can check, and the exclamation mark in "as she does now!" is a rare moment where the plain voice lets feeling break through.
The poem is worth reading for that restraint. It does not explain why the speaker has held on to this girl, or say what became of her, or how many years separate then from now. It trusts a few sounds, a flicker of white and a three-word warning to hold the weight. That leaves a lesson about how we tend to see other people. We judge them in the moment, often unfairly, and only later, sometimes much later, understand what they gave us.