So, last night I flopped a book down on my computer. I didn't notice it at the time, but it popped off the “N” key. Luckily, when I opened it this morning all four pieces were still there.
Directions: Top means toward the display, bottom means toward the touchpad.
The pieces, for lack of better nomenclature, are:
The key surface (the part your finger presses on)
The inside part
The middle part, with small horizontal posts on the outside left and right edges part way back from the top D. The outside part, with small horizontal posts
You need to figure out how this pieces fit together and what parts catch where.
It took me a lot of fiddling, but eventually I figured out that it if I put the outside part on top of the middle part, flattened them, set them in the space where the key goes, and gently slide them toward the bottom that the bar at the top of the middle part and posts on the outside left and right edges of the outside part would slide under the cuts in the thin metal pieces that stood up from the base of the keyboard. Then I hooked the bottom of the inside part under the bar on the bottom of the middle part and gently pressed down on the front of the inside piece until it clipped on to the bar of the on the front of the middle piece. Once this was done, I had, viewed from the side, an X with a bar across the top. Then I slide the key surface onto the X from the bottom, making sure to hook the back of the X under the lip on the bottom underside of the key. Then I gently pressed down on the key surface until the clips on the front of the key surface clipped onto the front of the X.