(An ongoing scheme remains face up until it's abandoned.)
Each opponent can't cast more than one spell each turn.
At the beginning of your upkeep, if no opponent cast a spell since your last turn ended, abandon this scheme.
6/15/2010 Players can’t respond to the action of setting a scheme in motion. That means that if this scheme is turned face up, your opponents can’t cast spells before the static ability takes effect.
6/15/2010 If any of your opponents cast a spell during your upkeep or draw step, that player can’t cast another spell during the turn this scheme is set in motion.
6/15/2010 The scheme is abandoned if all your opponents refrain from casting spells during their entire turn, and during your subsequent upkeep before this scheme’s last ability resolves. They may still activate abilities and perform special actions.