A soothing melody lures a young girl out of her house and into the middle of the woods.
Ichabod receives an Amber Alert and pictured is Sara Lancaster-Weiss (age 10). The same girl that walked into the woods. Abbie knows the family well.
At the Lancaster-Weiss home, we learn the woman was Abbie and Jenny's case worker when they became wards of the state. She helped her through a difficult time. Abbie promises she will find the little girl.
As they walk through the woods they spot blood and a flute made of bone. When Icabod plays the flute, Abbie instantly falls into a trance-like state. He now understands the creature they're dealing with is a Pied Piper.
Abbie agrees to be bait in order to find Sara. Instead of the Pied Piper they run into Nick Hawley. Hawley was in search of a high value artifact, the bone flute when he spotted the little girl and was attacked by the Piper.
He informs Abbie and Ichabod about the Lancaster curse that dates back to 1778. Daniel Lancaster hired a mercenary to take out the British soldiers at his estate who had become too friendly with his female help. The Piper did his part but was later betrayed by Lancaster and killed.
Since that time whenever a Lancaster girl turns 10 years old (the age the bones are the right size to create his instrument), the Piper lures her out into the woods to her death. Since less than 36 hour have passed, Abbie believes there's still time to save Sara. She makes a deal with Hawley, help them bring Sara back safe and the bone flute is his. He agrees.
Elsewhere, Irving is researching the end of days when he has a vision of himself killing for the Horseman of War.
Our heroes arrive at the Piper's lair and make their way underground. It isn't long before they locate Sara but the Piper attacks and moves with supernatural speed. Hawley uses an explosive to distract the Piper while Abbie and the little girl make their escape. More explosives cause the lair to collapse.
Once they're clear from danger Hawley demands the flute. He's not interested in hunting the Piper down. Abbie keeps her end of the deal, but snaps the bone flute in half first.
Sara is returned safely to her parents but her mother seems disappointed rather than grateful.
Using police records Abbie verifies that every generation for hundreds of years a Lancaster girl has gone missing. In 1936 one girl was recovered but her siblings soon died of a mysterious fever.
Abbie and Ichabod come to the conclusion the mother must sacrifice one child in order to save the others.
When they return to the Lancaster home, the children are already sick and Beth has taken Sara into the woods to deliver her to the Piper. Abbie confronts the woman and begs her to let them help her. She agrees just as the Piper appears to claim his prize. Ichabod and Abbie follow the creature eventually finishing him off.
At Tarrytown psychiatric ward Irving attempts to fire Parish as his lawyer. The Horseman of War informs Irving that leaving his employ is not a good idea. Irving recalls signing the contract in blood.
At a local tavern Hawley meets with a Hessian and turns over the broken bone flute. The buyer is none other than Henry Parish, who crushes and grinds the bone to dust.