In a word, as our Pretty Little Liars critic expressed last night: WOW.

Following weeks of stalled developments and storylines that never really went anywhere, "Monsters in the End" delivered numerous shocks, surprises and advancements, highlighted by a certain key and an eerie flashdrive.

How will this impact events on the finale? Will we discover who killed Alison? The following promo offers fans their first look at the spring finale. Get excited for it now...

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.