Episode Summary from syfy.com:
When we last saw Audrey she was about to begin the process of restoring Duke Crocker's previous Trouble: His family curse. The Crockers have always been able to remove a Trouble from a Haven family's entire bloodline by killing a member of that family. A Trouble Duke shared until he killed his own brother.
Previously, Audrey and Duke decided to restore his Trouble so that Duke could kill Ben Harker, thereby end the Harker family curse that makes someone in Haven die whenever a member of the Harker family cries. Since William had activated the Harker Trouble in Ben's newborn son, people were dying frequently.
In the present, Audrey touches Duke's chest and something happens. Not only does she bring back Duke's Trouble but she also remembers who she really is: A seemingly ageless and evil woman named Mara. When she finally remembers herself, William can feel it and goes to meet her.
Meanwhile, Duke uses his freshly restored Trouble to kill Ben Harker and end the Harker curse but he also feels Audrey remember her past so he knows to watch out for any sudden changes in her behavior.
Audrey confesses her memories to Nathan and hatches a plan to use her memories against William. A plan that almost backfires when William senses her intentions. Luckily, Audrey is strong enough to resist the pull of Mara's memories and gives Nathan the opportunity to subdue her … and therefore William.
Across town, Vince Jennifer, Dwight and Duke make the startling discovery that Dave (like Jennifer, William and Audrey) is from another dimension. Dave, however, doesn't want to help open the portal, even to get rid of William. He's scared of being sucked into the void himself or, worse, letting an evil greater than William out.
At the gateway underneath the lighthouse, Dave tries to sabotage the proceedings but he is thwarted and Jennifer is able to get the dimensional doorway open. Dave is sucked into it but Vince and Dwight save him, just before Nathan shoves William into the portal.
After William vanishes, Jennifer passes out, Duke starts bleeding from every orifice and, worst of all, Audrey reverts to her true self: Mara. Before anyone can react Mara commands them all to help her rescue William from the beyond. She wants him back.
Episode Summary from en.wikipedia.org:
William continues his plan to turn Audrey back into her original self. Meanwhile, the rest of the gang finds out that some doors are better left unopened.
Please use this thread to discuss the series' fifty-second overall and fourth season thirteenth episode The Lighthouse. Rule: Please keep spoilers limited to those revealed during the series up to this episode only.