The Mystery Duck's Story is the fourth story in Where's My Water?. The Mystery Duck's Story is an optional In-App Purchase that puts a magical twist on Swampy's Story. The regular Swampy Ducks are replaced with the teleporting and levitating Mystery Duck, or the water consuming Mega Duck, or a crew of ducklings. If the player doesn't collect the duck(s) on a level, S/he can not go onto the next. The pack cost USD 1.99.
The player can try the first five levels of this pack for free.
The Mystery Duck has the same chapters and levels as Swampy's Story.
- The hidden Swampy level 'Planetarium' can be found in the Mystery Duck's Story but is called 'Mysterious Planets'.