In the film Dirty 30, the 30 is a key age in the life of every person. At that age you realize that you have stopped being young forever, something that is in charge of the administration, which leaves you no advantage because you are young and you put your feet on the ground.
Kate is about to fulfill them, to leave her youth behind and is not willing to let that happen like this, so that along with several of her best friends decides to organize a somewhat wild party.
Only 30 years are celebrated once and only once the youth is abandoned, so Kate is going to make it big, in a huge chaos in which little by little the past is going to join with the present.
The return of the past is not always a good idea, because we all have one and there is always something to hide, especially when we are young.