Avery Waldorf wakes up from a concussion to find a voice inside her head—an adventurous male voice belonging to Marcus, who doesn't know where he came from, but has an opinion on everything about her life. She just wants to work on her screenplay, go to her writing classes and flirt with the guy of her dreams, Nash, who is finally noticing her.
Marcus wants to get up at dawn, run, snowboard, and basically take over her life, and even her body at times. He thinks she's freaking hot and does not like Nash touching her. Marcus may be smart, talented at snowboarding, drawing and playing the guitar, but he's not real! When she needs help, she has to call Nash.

She can't tell anyone about Marcus without sounding like she's crazy. Meanwhile Marcus doesn't know where he'll go if he leaves her mind. Maybe she is losing it...