Spy-themed birthday parties are a popular idea, particularly for young boys. Amp up partygoers' anticipation for the top-secret fiesta by sending out spy-worthy invitations. If the invite list isn't too long, the guest of honor could cut out ransom note styled lettering from old magazines and paste them in the invitations.
For a little more fun, mix up some invisible ink or squeeze a bowl full of lemon juice. Have the birthday boy or girl carefully dip a fine paintbrush into the juice and write an invisible invite message. Since it would probably take too much time to write out all of the party details in the invisible ink, just scrawl a phone number, e-mail address or Web site URL that guests can use to get more details about the party.
And don't forget to include instructions on the envelope on how to read the secret message: Simply hold the paper up to a heat source.
Complementary Party Themes: spy, scavenger hunt, mystery.