Setting Up

Each player will be given a card. Two players will receive Werewolf cards, one will receive a Seer card, and the rest will be Villagers. Look at your card, but do not show it to anyone else - you must keep it a secret.

Two players are secret werewolves. They are trying to slaughter everyone else, the innocent villagers. But one of the villagers, the Seer, has mysterious psychic powers and can detect the taint of lycanthropy.

The Game: Night and Day

The game proceeds in alternating night and day turns, starting with the night.

Each Night, all of the players will be instructed  to close their eyes and go to sleep. All the players must close their eyes, and feign sleep, and must make loud noises, humming, fake snoring, etc, so that they will not hear what is going on. It is very important that everyone keeps their eyes closed until they are told to open them. Anyone caught opening their eyes before they are told to will be thrown out of the game. 

The two Werewolves will be instructed to open their eyes. The two werewolves should do so, and look around to recognize each other.

The Werewolves will be instructed to pick someone to kill.  The werewolves silently agree on which villager it will be. It is important they remain silent. The other players are sitting there with their eyes closed, and the werewolves don't want to give themselves away. Sign language is appropriate, or just pointing, nodding, raising eyebrows, and so on.

When the werewolves have silently agreed on a victim, and the moderator of the game understands who that is, they will be told to close their eyes. Everyone else must still keep their eyes closed until they are instructed otherwise.

Next, the Seer will be commanded to open her eyes. The seer looks around and silently points at another player. It is important to do this without drawing attention, the Seer doesn't want to be identified by the werewolves!

The moderator silently signs thumbs-up if the seer pointed at a werewolf, and thumbs-down if the seer pointed at an innocent villager. The moderator then says tells the Seer to close her eyes.

The moderator then tells all of the players to open their eyes, and indicates which person has been killed. That person is immediately dead and out of the game. They hand their card to the moderator, face down, without revealing what it was.

Each Day, all the living players must choose to lynch one of the other players they suspect to be a Werewolf. The Werewolves are pretending to be innocent villagers, and the Seer does not reveal her identity either, since if the Werewolves find out who she is, they will choose her to kill next, to protect their secret.  The Werewolves will conspire to cast guilt on innocent villagers and away from themselves. There are no restrictions on speech. Any living player can say anything he wants - truth, misdirection, nonsense, or barefaced lie.

Dead players should not speak at all. As soon as the sun comes up and the moderator indicates that someone is dead, he may not speak for the rest of the game. Similarly, as soon as a player has been lynched, she is dead. If she wants to protest her innocence or reveal some information (like the Seer's visions), she has to do it before the lynching is declared. No player may reveal their card, to anyone, except after being lynched.

As soon as the village agrees on a particular player to die, the moderator declares him dead, and that player then reveals his card, and the rest of the players find out whether they've lynched an innocent villager, a Werewolf, or (uh-oh!) the Seer.

Once a player is lynched, night falls immediately and the cycle repeats. Everyone closes their eyes, the werewolves (or werewolf, if one of them has been lynched) secretly select someone to kill, the seer (if alive) secretly learns another player's status; then the sun rises, one player is found dead, and the remaining players begin to discuss another lynching. Repeat until one side wins.

Winning

The humans win if they kill both werewolves.

The werewolves win if they kill all but one villager. At that point they can rise up and slaughter the villager openly and the game is over.

To Clarify...

The villagers are trying to figure out who's a werewolf; the werewolves are pretending to be villagers, and trying to throw suspicion on real villagers.

The seer is trying to throw suspicion on any werewolves discovered, but subtly (because the werewolves will almost certainly eat the seer if they find out who it is, as the greatest threat to werewolf national security). Of course the seer can reveal himself at any time, if he thinks it's worthwhile to tell the other players what he's learned. Also of course, a werewolf can claim to be the seer and "reveal" anything he wants. Living players cannot show their cards, after all.

The only information the villagers have is what other players say - and who dies. Accusing someone of being a werewolf is suspicious. Not accusing anyone is also suspicious. Agreeing with another player a lot is suspect, and therefore so is pretending not to agree with another player. Never voting to kill a particular player is very dodgy for both of them - unless it's the seer who knows that player is innocent.