Texas Hold'em tournament home game. I get dealt A-s and Q-d mid position. Saw the flop, called a bet. Saw the turn, called a bet. On the river comes the fourth diamond to the board. Me and one other player, I check, he bets. I look at my hole cards to find one card missing. The one remaining is the Q-d filling my flush. Is it legal to continue to play and showdown with only one card? Where can I find the answer?
Rules of poker:
You must protect your own hand at all times. Your cards can be protected with your hands, a chip, or other object placed on to p of them. If you fail to protect your hand, you have no redress if it becomes fouled or the dealer accidentally kills it.
You must keep your cards in view of the dealer.
I get it was just a home game but protect you cards is your responsibility. You deserve to forfeit the hand - even in a home game.
Home Games often have their own rules partly defined at the start of a night (or otherwise generally known by the players), and partly impromptu. It would be up to the host to resolve this incident. Otherwise: FIND THE CARD!
Sounds like somebody tried to cheat you. But as @Paparazzi said, you are responsible for your cards so you could reasonably expect to be folded out.
The fact is it was a home game and crap happens sometimes. If your other card cannot be found, the fairest way would likely be to look at every other card in the deck and on the table and if the only missing one is the queen of diamonds, you have won. As this is unfair to other players who mucked, this should preferably be done by a person not in the game.