Danny is desperate to pass a standardized test called the C.A.T. After a fight with a ghost from the future sent by the mysterious Clockwork puts the answers to the C.A.T. in his hands, he decides to cheat in hopes of securing an easy pass to a great future. After fighting another ghost from the future, he, Sam, and Tucker discover that Danny cheating leads to a horrible future where after the death of his family and friends, Danny grows up to be Dark Danny, the evilest and most powerful ghost on the planet who terrorizes the world. Upon discovering Clockwork's interference, Dark Danny tries to make sure Danny's horrible future comes to pass by trapping Danny in his timeline, while he returns to 14 year old Danny's time. To save his friends, family, and future, Danny must escape back to his timeline with the help of the future version of Vlad (who is indirectly responsible for Dark Danny's creation) (thetvdb.com)