Tell your audience that you have a magic deck of cards that can vanish and reappear. Display a pack of cards in a case, and then withdraw the cards from the case. Leave one card in the case, mentally noting the suit and number. Distract the audience from realizing you've left a card in the case by flourishing the pack of cards in your other hand. Slip the case in your pocket.
Remove five cards from the top of the deck and quickly read the card names aloud, substituting the suit and number for the card in the case for one of the five cards. You can briefly flash the cards at the audience while saying the name, but show as little of the cards as possible. Request that someone in the audience write down the five names.
Replace the five cards in the deck. Hand the deck to the audience and ask them to locate all five of the cards.
Try as they might, the audience will not find one of the five cards in the deck. Pull the card case from your pocket, and let the missing card slide out in full view of the audience.