Sony Computer Entertainment America added a new chapter Friday to popular video game "The Last of Us," filled with combat against zombie-like infected people and tailored for PlayStation 3 consoles. "The Last of Us: Left Behind" is the game's first single-player downloadable content and is billed as a prologue to the award-winning action title that sold more than three million copies in the three weeks after its release in June. "Left Behind" puts players into the role of the game's young heroine, Ellie, and strives to "flesh out" experiences that turned her into the character introduced last year. Made by Naughty Dog studio and published by Sony, the game plays out in the aftermath of a pandemic that turns much of the population into zombie-like creatures that kill with bites. Players were gripped by an intensely emotional dynamic between the main characters struggling to survive. "In 2013, players across the world fell in love with Ellie," said "Last of Us" creative director Neil Druckmann. "She's been described as a bold, courageous and endearing young woman who overcame extraordinary emotional and physical challenges." The PlayStation online shop priced "Left Behind" at $14.99. It is free for players who bought "season pass" subscriptions with the original game.