Oracle Text

Whenever you cast a creature spell, you may pay 1. If you do, return target creature to its owner's hand.

Card Rulings

4/1/2008 A “creature spell” is any spell with the type Creature, even if it has other types such as Artifact or Enchantment. Older cards of type Summon are also Creature spells.
8/1/2008 The ability is put on the stack immediately after you cast a creature spell, which means the creature that spell will become won’t be a legal target.
8/1/2008 The ability will still resolve even if the spell that triggered it gets countered.