Pretty Little Liars (season 7)

Let them say there is no woman friendship. Although, perhaps there is not. Four old friends managed to pick a fight with each other for a long time about their common friend Alison. They were arguing for a year. Then the girls decided to forget about it and to be good friends again. Just after the reconciliation the girls start to get strange messages from mysterious A. This stranger knows everything about them, all the secrets their lost friend knew. It is bad enough to know but the stranger is determined to uncover these secrets. Who does send this threats? Alison is dead. What if she is alive and plans some kind of incomprehensible game?