Ticket to Earth is a marvelous episodic adventure in which you play as the survivor, Rose, as she signs up with the Peace Keepers to help defeat riotous mining robots. The interesting bit here is the game's take on the RPG genre, twisting it so it's part RPG, part narrative, and part match-three in a way.
Apparently the sale has come in celebration of episode two's imminent arrival, so hopefully we won't have long to wait for that one. There'll be four episodes in total.
Honestly, it was one of the most surprising mobile games of the year so far, so I highly recommend checking out the review and of course the App Store page. Usually £6.99/$6.99, it's a bit of a steal at its current price.