The speaker sets out on a simple walk in the rain and ends up lost in thought. Under an umbrella, they watch ferns sway in the wet and think about their own feet, which keep pushing against stillness. The title, "Mission creep," names the joke: a plain stroll keeps expanding into bigger questions, like what ferns owe the world or what feet are entitled to do.
The images then drift in odd directions. Wisdom is imagined as something that grows on trees, then as gray paper, then as a "head-sized tumor / emitting hornets," a startling, unsettling picture of how thinking can swell and sting. The poem settles on something small and exact: rain beading on a jewelweed leaf, gathering into its veins, a tiny world held in a drop.
The mood is playful, curious, and a little uneasy. By the end the speaker's pace has slowed "to a creep," so the walk's mission has quietly become paying attention.