In "Sister Issues," Holly feels inferior to her younger sister Stephanie (Jamie Denbo), a heart surgeon, and is determined to show her how well she's doing. Holly thinks she found the perfect way to impress Stephanie when the Mystery Girls are hired to find a missing young heiress. With some help from a selfie, they track her last location to a biker bar. Once they arrive and begin snooping around, Charlie discovers that Nick actually faked the entire case in order to cheer Holly up. The girls decide to keep up the charade once Stephanie arrives, but when they push around the wrong biker, things go from bad to worse.