Why doesnt my sims late night not work? please read my details!?

so i want to play sims late night so i put the disk on and pressed the play button that gets the game up and runnin....so when i get to the screen where it shows your person and their house...or all the other families you have (i only have one person **kinda new at this) well anyways it only shows my person from the regular sims 3.....WHERES MY SIMS LATE NIGHT PERSON....? what am i suppost to do?