Forty Thieves is a two-deck solitaire with a reputation for being tough. Every card in the columns is face up, so you can plan ahead, but you move one card at a time, build only in suit and never get to redeal the stock. Wins come from careful planning rather than luck.
The goal and the layout
Your goal is to move all 104 cards onto the eight foundations. Each foundation holds one suit, built up from Ace to King, so every suit gets two.
Forty cards are dealt face up into ten columns of four. The other 64 cards form the stock in the top-left corner, with the waste pile beside it and the eight foundations to the right.
Moving cards
Build down in the same suit: a 6 of hearts can go on a 7 of hearts, but not on a 7 of diamonds.
Only the top card of a column can move, one card at a time.
Any card can go into an empty column, not just a King.
Cards on a foundation stay there.
Drag a card to move it, or double-tap it to send it to the best spot: a foundation first, then a column.
The stock and the waste
Tap the stock to turn its top card onto the waste. The top waste card can be played to a column or a foundation. There are no redeals: once the stock runs out, it is gone, so each card you turn has to count.
Cards that nothing else could need go up to the foundations by themselves, and undo takes back your last move or draw.
Classic and Relaxed modes
Classic follows the traditional rules: one card at a time. Relaxed lets you move a run of same-suit cards together, but only when you have enough empty columns that you could have moved it card by card anyway. One empty column moves two cards, two move four and three move eight. Moving into an empty column does not count that column. Your records are kept separately for each mode.
Tips for winning
Getting an empty column early matters most. Look for short columns you can clear.
Do not fill an empty column without a plan: it is your only parking space.
Before you turn a stock card, play everything useful from the columns, then check whether the new waste card has somewhere to go.
Avoid burying low cards of a suit under high cards of another suit. Aces and twos trapped deep in a column are the usual way games are lost.
Building long same-suit runs in Classic can trap you, because they can only be taken apart one card at a time.