Lefty discovers an old mirror in his attic with his brother, Max. Upon realizing that turning the mirror's light on turns anyone standing in front of it invisible, Lefty becomes obsessed with becoming invisible. He fights with Max over the opportunity to have a turn at becoming invisible, and he eventually begins sneaking off on his own to become invisible and pull pranks on Max. He continues becoming invisible even after Max suspects the mirror is malevolent and begs Lefty not to use it.
Once a friend of Max's, Zack, boasts about staying invisible the longest, Lefty joins the competition to see who can stay invisible to longest. He breaks Zack's record on his own, eventually staying invisible for close to fifteen minutes.
During that near-fifteen-minute run of being invisible, Lefty is presumably sucked into the mirror and forced to trade places with his reflection. Max and his mother both notice physical differences in Lefty after this.
Lefty's reflection, now free, calls and invites Max's friends, Zack, Erin, and April, to an invisibility contest that Max had canceled, so that their relfections can trade places with them and escape the mirror.
For an unknown reason, after Max escapes the mirror and is beind held captive by Zack and Erin's reflections, Lefty's reflection comes in and throws a softball at the mirror, shattering it and sending Zack and Erin's reflections back into the broken glass or the mirror to switch places with the real Zack and Erin. Lefty's reflection begins to be sucked into the mirror like Zack and Erin's reflections, but he hangs on to the door frame and escapes switching places the real Lefty.
Max is outside playing catch with Lefty when he realizes Lefty is pitching right-handed, revealing to himself and readers that the real Lefty never made it out of the mirror.
Lefty is hyper, rambunctious, and competitive. He likes to play pranks on his older brother, Max. This and his competitiveness result in Lefty being trapped in a malevolent mirror.
Lefty is left-handed. Max states that his brother, Noah, is called "Lefty" because he is the only left-handed person in his family.