Intelligence is a Patience game which uses two decks of playing cards mixed together. It is basically a two-deck version of another solitaire game La Belle Lucie and its game play is somewhat closer to the parent game than its cousins House in the Wood and House on the Hill.
First, 18 piles (or fans) of three cards are dealt. During this deal any ace encountered regardless of where it would end up in the pile will be moved to a foundation and be replaced with another card. As they become available, the other aces are placed on the foundations, which are all built up by suit.
The top cards of the piles are available to be built on the foundations or on each other's piles on the tableau. When building on the tableau, the cards are built either up or down by suit. Aces cannot be placed over kings, however, and vice versa.
When a gap occurs, it is immediately filled by three new cards from the stock. This is the only way cards from the stock are introduced from the game and the only way spaces are refilled. As in the original deal, any ace that comes up is immediately placed on the foundations.