Source: Player's Handbook II
You have studied a single spell in-depth. Your expertise grants you formidable though narrowly focused arcane mastery.
Prerequisite: Knowledge (arcana) 9 ranks, ability to cast arcane spells.
Benefit: Choose one arcane spell that you can cast to be your thesis spell. When casting that spell, you do so at +2 caster level. When you apply a metamagic feat other than Heighten Spell to that spell, the enhanced spell uses up a spell slot one level lower than normal. For example, an empowered thesis spell uses up a spell slot one level higher than the spell's actual slot (rather than the normal two levels higher).
Special: You can gain this feat multiple times. Its effects do not stack. Each time you take the feat, it applies to a new spell.