The speaker begins by marvelling at herself. "Most wonderful and strange it seems" that someone so recently "tost / High on the waves of passion and of pain" should now lie "calm and still and silent." The poem is about the strange quiet that follows emotional extremity. It does not celebrate that quiet as peace. It examines it warily, and its last line admits that the calm hasn't settled anything.
The first eight lines are a single sentence, and the structure carries the meaning. The speaker, "I," arrives in line 1, but the main verb, "should lie," is held back until line 7. In between come two "Who" clauses recalling the earlier turmoil, so we are carried through the storm before we are allowed to rest. The sounds are heavy and physical: "aching heat and wildly throbbing brain." The rhyme scheme backs this up. "Pain," "brain" and "vain" come in a row, like a pulse that won't stop. The unusual pattern of the octave is a b c c c b a a, so the poem leaves the usual Petrarchan arrangement behind. Even the "darkness" the speaker peered into is full of desperate logic: all things found there were "vain / ... if but One thing were lost." The capital letter on "One" is telling. Whatever was lost is never named, and the capital makes it feel absolute, the single thing that gave everything else its value. The title, "Sonnet," withholds specifics in the same way, and the reader is left with the shape of the loss and none of its details.
The octave ends in near-stillness. "Watching and waiting, --waiting passively" opens with a trochaic stumble and then repeats its key word, so the line itself seems to wait. Its final rhyme is the faintest in the poem. "Passively" is supposed to echo "I" and "lie," but its unstressed ending barely sounds, and the line goes slack just where the speaker has gone slack. The word "passively" also reads like a quiet self-criticism, since this calm is a lack of action.
At the turn, the imagery changes. The sea of the first half ("waves") gives way to land: "long, grey flats expanded, dim and bare." This is a landscape after the water has withdrawn. The dark has "faded" but no bright dawn replaces it, only a dull light that shows how little is there. The words "dim" and "bare" make the new clarity feel more like exposure than relief. The speaker now sees "through the changing guises all things wear" to "Inevitable Law," and this too has a capital letter. The two capitals mirror each other: the personal absolute, the "One thing," has been replaced by an impersonal one. She no longer feels her way through the world and instead "recognise[s]" how it works, a cooler, more intellectual verb. The poem suggests that this understanding is a way of surviving, but it offers no warmth.
Then comes the ending. "Yet in my heart a hint of feeling lies / Which half a hope and half a despair." The line has no verb. We expect "which is," and the missing word makes the sentence hang unfinished, as if the feeling can't be fully stated. The word "hint" is small and tentative, and "lies" echoes the earlier "lie," as though even this stirring is lying still. The final rhyme, "despair" with "bare" and "wear," quietly ties the feeling to the barren landscape. Hope and despair are weighed in perfect balance ("half... and half"), and the poem declines to tip the scale.
What makes the poem worth reading is this honesty. A sonnet's turn usually delivers an answer or consoling insight. Here the turn delivers clear sight, and clear sight turns out to be ambiguous. Poems about suffering tend to focus on the storm, but this one is about its aftermath, the flat, uncertain stretch when the feeling has drained away and nothing has yet replaced it. In fourteen lines it shows that calm can be unsettling in its own right, and it ends on a feeling it cannot name.