Here's the invitation, which I put inside a small envelope made from a large manila envelope. The font is Old Typewriter, found here.
Games included a treasure hunt and hot potato with a "grenade" (easter egg covered in duct tape). Here's the cake, a total non-sequitor (gumball machine) but that's what the ninja wanted:
I finally figured out this mysterious Viva paper towel method of making the cake look like it's frosted with fondant without having to actually eat fondant. After cake and presents and another impromptu treasure hunt, we sent the kids to the basement, threw Cody Banks 2: Destination London up on the projector, and sat down for a tiny rest. After 15 minutes, I heard this: "They said we were going to have popcorn and it's been like 2 hours and WHERE IS THE POPCORN?" That was my cue to get up and pop the promised corn.
On the way out each agent got some Pixi sticks, a secret agent badge (dollar store) and magnifying glass (ditto) wrapped up in some old engineering plans from dh's office. I think we all had fun. And I was grateful for the shop-vac when I saw the basement.