Daphina's Spell Converter

You attempt to steal the magic of a spell from a creature as it is releasing it and convert it into your own magical force. If the spell's level is 3rd or lower, you instantly convert the spell and regain a first level spell slot. If the spell's level is 4th or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. Upon success, you convert the spell into a spell slot equal to half the initial spell's level, rounded down. On a failure, the initial spell continues as usual. 

At Higher Levels: When you cast this spell using a spell slot of 5th level or higher, you may convert spells of a level one lower than the level of the spell slot spent without needing to make a saving throw.