After Rosettes immolated exit, both Bo and Rainer feel the crushing weight of the wanderer's power as the dark entity struggles to unfasten the final shackles holding him with Hel. Yes, you're reading that correctly, the wanderer's prison is the Norse world of magic and chaos, just one "l" off from the whole fire and brimstone aesthetic.
Bo, Rainer and Trick have forged an uneasy alliance and are contemplating their next move, when an origin-seed powered Massimo bursts onto the scene brandishing a full set of brand new Fae powers. A few energy blasts and some broken furniture later, Massimo has Rainer at his mercy. Unfortunately for Bo's latest love interest, the duper-human Druid has mercy in incredibly short supply, and Rainer's neck is snapped before we even reach the halfway point of this tumultuous season finale.
With the death count rising, Tamsin goads Bo into draining some of her Chi so that she will be powerful enough to face whatever challenges lay in wait. Meanwhile, Kenzi discovers an ancient passage foretelling that Bo must sacrifice her heart in order to seal the gates of Hel and prevent the rising of her father.
We learn that Bo's unique standing in the Fae community did not come without a cost. Aife, Bo's mother, was given to the Dark as penance for actions taken against the Morrigan in the name of the Blood King. And while Trick had been resigned to the sacrifice of his only daughter, he had not anticipated that Aife would have been kept alive and meant to breed with the Dark-aligned man who would be the wanderer. As a result, Bo is able to both suck and blow chi from multiple beings in unison. No other Fae, even those enhanced with the power of the origin seed, are able to manage this trick.
Bo is crestfallen over the loss of Rainer, but Dyson vows to serve her as his queen, and her resolve to end the latest threat to her world is steeled. The lovers turned comrades enter the temple of the priestesses of Epona, where the portal to Hel has opened, and are confronted by a steady stream of revenants (that's Fae zombies for any newcomers).
Bo, almost instinctually, takes in the collective chi of the horde, but instead of sapping their strength, she is imbued with a darkness from the void that tickles her dormant potential to be an agent of evil. Dyson is able to snap her out of it with one of their trademark scruffy make out sessions, and she instructs him to stay behind to stem the flow of shambling undead Fae while she heads off to confront Massimo and attend to her other recently neglected lover, Lauren.
Despite her hybrid blood and her succubus strength, Bo is absolutely no match for Massimo, who revs up a siren scream of his own as a twisted instrument by which to incapacitate Bo. That is, until the Morrigan saunters onto the scene. Regardless of his strength and her weakened state, Massimo is still powerless in the face of his mother. Misreading Evony's intervention, Bo quickly takes her as a hostage and presses a knife to her throat, temporarily putting a pause to Massimo's onslaught.
But Massimo has picked up even more new tricks, and turns Bo's chi sucking ability against her. Quick as ever, Bo dodges the attack so that it lands squarely on the now-human-Morrigan. Massimo is distraught, but is unable to sever the syphon, a trick Bo only perfected after a lifetime of unintended murder. Bo taunts Massimo, needling him with the notion that if he really loved his mother he'd be able to turn his power off. But despite his struggle, Massimo is not up to the task. Evony crumples to the ground and the crazed druid is defeated by his own grief. In a final bid for his mother's approval, Massimo allows Bo to drain his chi, and do what only she can do – use it to restore life to Evony.
Lauren stays behind to clean up the rest of Massimo's mess, while Bo has a sudden realization that sends her barreling towards her friend on the battlefield at the gates of Hel. Dyson, Tamsin, and even Trick are valiantly holding off the ever-growing waves of revenants, but it's Kenzi who has Bo's attention. Having finally deciphered the prophecy, Kenzi finally sees her place in it. Kenzi is Bo's heart. No werewolf, or doctor, or cursed mystery man – no matter how hot the sex may have been - can represent everything that Bo needs to stay grounded, sane, and whole like her best friend.
Kenzi walks serenely to the portal's mouth despite her friends' family's protestations, and succumbs to a warrior's death, promising Bo that she will find her in Valhalla.
With the wanderer driven back, Tamsin does what Valkyries do best, and escorts Kenzi's soul to the hall of fallen warriors.
All may seem sorted, but when Dyson retrieves a harried Tamsin from the gates of Valhalla, he is stricken with panic and dread. Tamsin reports that Kenzi is missing, and warns Dyson not to allow Bo to unearth the second hellshoe.
Bo, meanwhile, rests a bouquet of sunflowers on Kenzi's grave. She knows in her heart of hearts that this is not the end of their story, and, standing tall, proclaims that whoever's been messing around in her life better be afraid, because she's coming armed with a can of whoop-ass, succubus style!