It's as simple as black and white.

Imagine a chess game. Two opponents sitting in a room trying to manoeuver their chess pieces in to a winning pattern that will defeat the other player.

One opponent is White. He starts first and has to play by the rules of the game. He wants to win because the chess board is his. If he wins, he can relax in the room and think of ways to make the chess board nicer, or perhaps make a new chess board in a different room. He starts off with the usual pieces and can only upgrade his weaker pieces by getting them to the far end of the board. If they get there, without being killed or sacrificed, they will turn in to some of the strongest playing pieces possible. However this is very rare. To start with White didn't know he was playing a game, and it was only when he started moving his pieces across the board that he found his opponent.

The other opponent is Black. He started second and doesn't have to play by the rules. However, he can only cheat when White doesn't notice. He can't stand chess but has to play. He has no choice. If he wins, he gets to burn the chess board and escape from the room he is in. His cheating can involve upgrading pieces, moving them illegally and also corrupting White's pieces, in effect making them his own. White wants everything perfect, so even a hint of discolour on them will cause White to sacrifice them before any another piece. Black knew there was another opponent, but at the start was too busy trying to find a way out of the room. He started off a few moves behind White, but is starting to get the hang of the game now. He still hates the game though, bitter that White has trapped him here until one of them wins.

An extra layer of complexity is that each player can go back and forth in time along the duration of the chess game. This mainly allows Black to change something subtlely which could have significant effect later on in the game. White tries to follow these changes, either by pointing out when Black cheats, or by manipulating Black's move so that it helps him later on instead. However, whilst he is studying the latest change that Black has made and its ramifications, Black is already half-way down the board and ready to make another move.

Finally, just to complicate matters there is a third person watching the game from the room's doorway. He makes sure that no one can leave the room until the chess game is decided upon one way or another. His other purpose was to make the game last longer so the outcome was never inevitable. He has a stack of chess pieces that come from the other rooms in the house. Occasionally, when the mood takes him, he chooses a piece at random and throws it on to the game table. He can also go back and forth in time and watch the events as they are happening. However he prefers not to. Instead he likes to catalogue all of the changes that have ever occured on the chess board. He knows when Black cheats, never missing a trick. But he keeps that knowledge to himself.