A woman watches the sun go down beside her lover, who is strangely still. While she watches, she takes a gun from her pocket, and the poem follows her as she trembles, counts down to one, and tries to steel her nerve. We never see the shot. The poem stops before it, which leaves the outcome open.
The triolet form does a lot of the work here. Its repeated lines mean the opening image, the sinking sun and the still lover, keeps coming back like a thought she can't escape. The repetition feels obsessive, and it traps the reader in her moment of hesitation. Even the stillness of the lover starts to sound ominous, since the poem never explains it. The subtitle, "blackmail," hints at a motive, though the poem itself gives us no details.
The mood is tense and quiet. Her fear and determination pull against each other, and the setting sun suggests that something is ending.