In a Christmas party, Flash Sentry made up a story for a movie the people failed to watch.

Young Flash Sentry is a black sheep of the family. But when he was left home by accident, he is left to thrive things on his own.

But, Gotham's greatest criminals, Joker and Harley Quinn have been stealing around houses with families away from vacations. And his house is next, it is up to him to defend his house and face the city's greatest criminals...Home Alone!