The Man Who Knows by Liam Montier and Matt Lingard

The Man Who Knows is a self-working miracle with a devious method that will leave a lasting impression on all audiences.

A mysterious red envelope is introduced and left in clear view. You then show five gorgeous, full-color postcards with some of the most famous magicians in history: Thurston, Alexander, Kellar, Von Arx, and, of course, Harry Houdini. Each one is placed in a separate black envelope. These envelopes are them freely mixed by a spectator.

You then present a deck of cards (which can even be borrowed). Your spectator is invited to select an envelope, as well as one of the cards. The idea behind the effect is that you will perform a magic trick in the same style as the famous magician they choose.

They end up with "Alexander" (aka "The Man Who Knows") and the Four of Clubs. As Alexander was a mind reader and mentalist, you then proceed to make a prediction.

You open up the red envelope to show that you knew they'd choose Alexander. However, upon closer examination, they also realize that their playing card has been revealed in his crystal ball.

Two versions are available: the "Standard Version" featuring mini-postcards and the "Pro Version" featuring double-sized postcards for parlor magic shows.