The Unknown Card by Nick Trost

You fan out six cards to show three face-up Fours and three face-down cards. The cards are turned over and re-fanned to show three Tens. An “unknown” card is removed from your pocket and inserted into the fan. You now deal the Fours face down to a spectator while you hold the Tens and the “unknown” card. Your cards are squared, turned end-over-end three times, and re-fanned. The “unknown” card is pocketed. The Tens are now gone—faces and backs of blank-face cards are shown! The spectator's cards are turned over and the Fours are gone!