The girls are reunited when they each begin receiving threatening messages from someone named "A," suggesting Alison is actually alive - and watching them.

The presence of Mrs DiLaurentis continues to unnerve those around her, especially when she gives Hanna a parrot, whose gift for mimicry provides an insight into Alison's last days.

Hanna worries that her mother is keeping a dangerous secret and is determined to protect her at all costs, which leads to an uncomfortable meeting with Detective Holbrook.

Holbrook's partner, Lt Tanner, comes to town, intensifying their investigation into the Liars and their possible connection to Wilden's death.

Spencer and Emily make plans to visit a nearby college, but they have very different agendas for their time spent on campus.

Hanna's attempt to protect her mother gets her into hot water. Hanna has some explaining to do to her parents and the police after she's found with something she shouldn't have.

Hanna comes up with a plan to save her mother from a conviction and turns to the only person she thinks can help: Mona. Caleb tries to convince Hanna that Mona can't be trusted.

Paige throws Emily a surprise birthday party with even more surprising guests - Jenna and Shana. But it's the actions of "A" at the party that lead to the biggest shock of all.

Still living at a motel, Emily is taken aback when Ali's mother offers to let her move into Ali's old room and is shocked when the other Liars insist Emily take up the offer.

After uncovering evidence that suggests "A" is hiding out closer than realised, the Liars step up their investigation into their most recent suspect. Hanna continues to crumble.

An intriguing riddle from "A" has the Liars hitting the road and heading to Ravenswood, where they are surrounded by some familiar faces.

Aria, Emily, Hanna and Spencer crash the Ravenswood Founders Day Celebration after a clue in "A"'s new lair suggests that Ali may indeed be alive.

Armed with the knowledge that Alison is alive, Aria, Emily, Hanna and Spencer now have more questions than ever before.

Now that Hanna has shared with Aria, Emily and Spencer that she has Ali's diary, the girls hope it can shed light on their many questions.

Shana tells Emily that she has a message from Ali, but can Emily and the girls trust Shana? Shana ups the stakes and says that Ali wants to meet Emily, but only Emily.

Hanna's interest in crime novels helps her to come up with a plan to figure out whose body is in Ali's grave. Spencer is working overtime to decipher the stories in Ali's diary.

With Spencer's possible revelation about Board Shorts, she is now more determined than ever to prove her theory before bringing it to the other girls' attention.

This special black-and-white episode gives a nod to 1940s-era film noir as Spencer's numerous sleepless nights with the help of prescription pills start to take a toll on her.

Spencer is determined to finally tell Aria what she has found out about Ezra, but Emily and Hanna are worried about what it could do to their friend.

The Liars are concerned for Aria as they watch her crumble after learning shocking news about Ezra. Not knowing what is true or who to trust, Aria goes looking for answers.

Emily takes up the sleuthing reins as she searches for answers about Ezra and Mona. After confronting both, Emily tries to make sense of the heartbreaking situation.

Spencer is reeling about the memories from her 'lost summer', Aria is nursing a broken heart, Emily struggles with Paige's betrayal and Hanna attempts to get back into dating.

After years of questions and mystery surrounding the night Alison DiLaurentis disappeared, The Liars finally learn what really happened to her that September night.