Before you begin the trick: Take a full suit of 13 (any one) and lay them down on the table, face up, in numerical order. Tell a spectator to note the order of the cards. Square them up and hold them face down in your left hand.

Here's how it's done:
Having first shown the spectator the suit of cards in numerical order and then taken them back into your hand, keeping them face down ....

You say: "You must tell me exactly how to deal these cards so we can be sure they're thoroughly mixed"

Explain that the instructions you need from them are: "DEAL" and "DOUBLE CROSS". When they say "DEAL" you'll put one card on the table (face down) and when they "DOUBLE CROSS" you'll take the next card from the pile in your hand, put it under the first one (on the same pile) and then deal both of them together on the table (again face down).

You then follow their instructions and deal the cards exactly as they say into a pile on the table.

You square up the pile and then suggest that to be sure the cards are really well mixed, you do it once more.

Once again you follow their instructions and deal the cards as they say into a pile.

Then ...picking up the pile you say:

"You're now going to see that no matter what you tell me to do with the cards, they will only do as I tell them!"

Turn the cards over so they're face up and spread them out in a line. All 13 of them will be in the same numerical order as at the beginning of the trick!