A pair of contestants must find the highest sum of money contained in one of 24 numbered envelopes, each containing a randomly assigned sum of money between £100 and £100,000. This is done by correctly answering a series of multiple choice questions.
In the first half of the game, the contestants select four of the envelopes and these are each assigned to one of the four possible answers. In this stage of the game, the computer assigns the envelope containing the highest sum of money to the correct answer. The contestants then eliminate the three answers they believe are wrong. With each elimination, the associated envelope is opened to reveal the sum of money being discarded. The remaining envelope is handed unopened to the contestants to be used in the second half. This continues over six questions until the contestants are left with six.
In the second half of the game, the remaining envelopes that the players keep in the first half are assigned to answers, but now the lowest sum of money is assigned to the correct answer and the contestants must identify and eliminate it. One envelope is discarded with each question until the final question becomes a 50/50 choice between two answers. The contestants win the sum of money inside the envelope they do not eliminate.