The speaker goes looking for relief and finds only pain. "They said that I'd find water," the poem begins, but the cave they retreat into gives them blood instead. The cave works as a hiding place, somewhere to escape "all I thought I loved," though the poem doesn't say exactly why the speaker is running.
From there the poem builds its main image: the heart as a fortress under attack. The soldiers breaking in are the speaker's own friends and family, who now know that "I have sinned." The speaker doesn't say what the sin is, which keeps the focus on the shame and the sense of being judged by the people closest to them. The walls fall like those of a weakened kingdom, and the blood that "ran like a river" suggests a total, draining collapse.
The mood is bleak and fearful, with a feeling of being cornered and betrayed. The simple rhymes and steady lines make the despair feel quiet and resigned rather than loud.