Oracle Text

Return target spell or creature to its owner's hand.

Card Rulings

7/13/2016 Spells that can’t be countered can be returned to their owner’s hand by Unsubstantiate. They won’t resolve.
7/13/2016 A spell that’s a copy ceases to exist as a state-based action after being returned to its owner’s hand. It can’t be cast, and it never counts as a “card” in the player’s hand.