Dustin has a sister. One who's much cooler than Nancy, one who picks the guys up from AV club, and one who even sits in on their Dungeons and Dragons sessions from time to time. Gracie Henderson is the big sister every member of the party wanted, and she's without a doubt the best babysitter going. When Will goes missing and the guys drag her down to Mike's basement, rattling on about a girl with superpowers, she doesn't think things could get much weirder. Then she finds Steve Harrington in the mix...