Counterspell

Regular; Resisted by subject spell 
Nullify any one ongoing spell. It cannot “counter” spells that make a permanent change in the world (e.g., Extinguish Fire, Flesh to Stone, or Zombie), and it cannot affect permanently enchanted items, but it can counter spells cast using magic items. The “subject” of Counterspell may be either the subject of the spell to be countered or the person who cast that spell. 
Counterspell is a single spell – but to counter a given spell, you must also know that spell. Roll against the lower of your Counterspell skill or your skill with the spell being countered. You must win a Quick Contest with the target spell to cancel it. You can cast multiple Counterspells to negate an Area spell piece by piece.

Cost: Half that of the spell countered, not counting bonuses the other caster got for high skill. 
Time to cast: 5 seconds. 
Prerequisite: Magery 1.