He asked, she accepted. …would be far too simple!
We agreed about what, got stumped by how. (How to devise a collaborative surprise?) She had an idea: why not propose a proposal? But before she had a chance to take a chance, he took his chances! Naturally, she needed more time. He good-naturedly granted it. Plans spawned more plans (and people, places, props, puzzles): A book was made. Clues were laid. Friends came to aid. Finally, at the end of a puzzling day: She asked him to ask. He accepted (on the meta level). Then, and only then: He asked, and she accepted.
(Which was pretty simple, after all!)