On the fifth anniversary the Mikaelsons defeat, Marcel is king of the city and welcomes the unsired vampires to New Orleans, only to find they pose an unexpected threat to his rule, leading him to seek counsel from an unlikely source.

Finally awake, Elijah, Rebekah, Kol, Freya and Haley return to New Orleans in an attempt to free Klaus, who, in the meantime, is forced to face his fears by a hallucinated Camille. Marcel tries to undermine their efforts. Vincent continues searching for Adam, a lost boy, and identifies the enemy they enemy they are facing.

After five long years apart, Klaus attempts to reconnect with his daughter, Hope. Even as father and daughter bond, the rest of the family is still in turmoil. Elijah mediates a conflict between Hayley and Freya to determine the best way to protect the family. Meanwhile, in New Orleans, Vincent tells Marcel terrible secrets about his ex-wife, Eva Sinclair, even as they begin their search for a mysterious witch who plans to sacrifice a group of innocent children - including Hope Mikaelson.

Desperate to save her daughter, Hayley turns to Marcel for help uncovering information about the mysterious force that has set its sights on the children of New Orleans. While Klaus remains behind with Hope, Elijah and a reluctant Vincent join the hunt, which puts them on a dangerous collision course with an unlikely new threat. Finally, Freya and Keelin must put aside their differences as they embark on a journey that may alter the power dynamic in New Orleans forever.

After being marked by The Hollow's dark magic, both Klaus and Marcel experience the symptoms of a malevolent haunting, forcing the two adversaries on a violent collision course. Meanwhile, Hayley and Elijah head out to speak with Mary after Hayley uncovers a mysterious link between the dark magic and her former wolf pack. Finally, as an exhausted Freya risks her own life to cure Klaus' infection, a guilt-ridden Keelin must decide whether to honor her Hippocratic oath and help Freya - or flee the Mikaelson's forever.

When it's discovered that The Hollow has employed a mysterious servant to do its bidding, Klaus and Elijah host an elaborate party in order to lure the new threat out and uncover its identity. Feeling a sense of responsibility for The Hollow's resurgence, Vincent uses his magic to help the Mikaelsons root out this latest threat. Meanwhile, after uncovering information about who may have been behind her parents' death, Hayley turns to Freya to help unlock her memories from that fateful day.

When it's discovered that The Hollow's latest servant is on the loose, Freya places a protection spell on the compound, forcing Klaus, Hayley and Hope to remain inside. Meanwhile, Elijah takes matters into his own hands when Vincent is reluctant to perform a dangerous ritual needed to strengthen their defense against The Hollow. Finally, while Freya enacts a risky plan that brings her face to face with their latest threat, an unexpected twist leaves her life hanging in the balance.

Old wounds are re-opened when Elijah and Marcel are forced into an uneasy alliance. Together, they meet with Alaric who has tracked down a crucial artifact that could help in their fight against The Hollow.

When The Hollow sends a terrifying message to Vincent, he must team with Haley and Freya to embark on a desperate mission to stop the Hollow once and for all - even if it requires a heartbreaking sacrifice.

Rebekah and Kol return home to stand by their family against the Hollow. Freya recruits Hayley for a dangerous journey. Marcel leads a hunt for the Hollow. Kol considers the lengths he'd go to see Davina again.

When it's discovered that The Hollow is using a magical totem to fuel her power, Freya enlists Rebekah and Klaus' help to locate and destroy it. Elsewhere, an ultimatum by The Hollow puts Kol at odds with his own siblings, while an unexpected run-in forces Marcel and Rebekah to confront the growing tension between them. Finally, The Hollow's plan for Hayley leaves her in the fight of her life.

When The Hollow targets the most vulnerable Mikaelson, Klaus is forced to rely on Vincent, who believes he can use The Hollow's own dark magic to defeat their enemy for good. Meanwhile, as Marcel worries that Vincent's plan might backfire, the King of New Orleans decides on a deadly backup plan of his own. Elsewhere, after falling victim to The Hollow's manipulations, Hayley struggles to figure out Hope's future in New Orleans, while Freya must confront her darkest fear.

The Mikaelsons find themselves out of options as they face the all-powerful and un-killable entity known as The Hollow. With the life of Hope at stake, Vincent proposes a final, desperate plan - one that will force Klaus, Elijah, Hayley, Rebekah and Freya to make the greatest sacrifice their family has ever endured.