Question: when does alison dilaurentis come back for good

title: Alison DiLaurentis
text: When Alison was about to get her life back , Courtney 's friends warned Mrs. DiLaurentis that `` Alison '' was missing . Jessica then assumed that Courtney ( Alison , actually ) did something against her sister 's life and sent her back to psychological hospital . Meanwhile , masons filled the hole where Courtney 's body was buried to build a gazebo . Hours later , `` Alison '' was reported missing . Three years later , Courtney 's friends began to be pursued by someone named `` A '' who knew her greatest secrets and threatened them constantly . Months later , Mona Vanderwaal , a classmate of the girls and Alison , was revealed to be `` A '' . Soon after , Alison took the reins of the game and began to chase the girls , seeking revenge for having everything she always wanted .