The poem opens with blood in the night and a quiet decision: "they say nothing about it to her." We never learn whose blood it is or who "her" is. The title, "First blood," might hint at a first menstruation, a first wound, or the first casualty of something larger, but the poem leaves that open. What it makes clear is the secrecy. Something has happened, and the adults carry on around it.
They sit down to dinner in a room full of "delicate pictures," a polite, hushed setting that sits strangely against what came before. Then the imagery shifts. Painted horses become "shelves for war," as if the room's decoration were quietly stacking up violence. The last lines send them "with great calmness / into the devil's wheat," a field that sounds both ordinary and sinister.
The mood is eerie and controlled. The speaker seems watchful rather than openly upset, and the calm itself is what unsettles us.