It is a stormy night at St. Crispin's Church, where nuns are ministering to the sick. One of these nuns is Derek's sister, Ingrid. A young girl approaches her, urging her to come to her dying mother and give her the last rites. She leads Ingrid through darkened hallways down to an unused area, where a woman wrapped in bandages lies in bed. Ingrid approaches, offering comfort, when she suddenly sees that the figure wears a Legacy Precept's ring! Gripping Ingrid hard, the figure rasps, "Sister Ingrid! We have a new mission for you, sister!" Ingrid is dragged away, struggling and screaming for help, by two mysterious robed figures as the young girl smiles enigmatically.
That same evening Derek is in the living room at the Legacy House, examining a Mycenean vase, when he gets a sudden vision of his sister's abduction-- the bandaged figure, the two in the robes, the young girl--and he hears her screaming. Convulsively smashing the vase, he cries out her name and hears a mysterious voice calling his. He rises to look for the source of the voice.
Mist forms under the door and becomes a strange robed figure. Derek demands of it what it has done to his sister, and it answers, "Nothing. But time is running out." It demands the Black Chalice, and warns that questions waste time, "a most precious commodity" that is running out fast for Ingrid. He has one day.
Soon after that Derek receives a call from William Sloan to say they've heard about Ingrid's disappearance. Sloan offers sympathy and assures him that the Ruling Council offers whatever resources Derek needs. When Derek claims he has everything in hand, Sloan reminds him that Legacy protocol prohibits negotiations with terrorists. This angers Derek, who demands why Sloan would think that he'd endanger the Legacy for the sake of one person, even his own sister. Sloan replies firmly that he knows Derek will do what's best.
Derek thinks back to an important meeting with his sister the year before, when she told him that while he has never forgiven their father, or himself, that she has and has found peace. When he told her that someone must be there to fight evil she urged him to gird himself properly for the battle.
At St. Crispin's, Derek sees the girl from his vision and follows her to a chapel. There she reveals in a frightened voice that she did it for her family's sake: "We're so poor; we needed the money." She begs him not to hurt her, and he assures her in surprise that he'd never do so. Then she points at the ring and accuses him of "being one of them." The person who took his sister had worn such a ring. He thanks her and leaves; she smiles--and vanishes in a puff of smoke.
Back at the Legacy House, Derek tells the team that one of his first assignments for the Legacy was the excavation of a great Aztec temple. The Aztecs believed the fire that animated the human body resided in the heart, and priests cut out sacrifice victims' still-beating hearts and squeezed the blood into the Blood Chalice, believing that whoever drank the sacrificial blood would be immortal and invincible. "Sorta like an Unholy Grail," Nick remarks, and that the abductors must believe they can trade Derek's sister for the chalice. They're wrong, Derek states in no uncertain terms, first because he'd never betray the Legacy, and secondly, "If they hurt Ingrid in any way there is no place they can hide I will not find them."
Derek's mother Barbara arrives at this point. Derek embraces her, then introduces her to Nick and Rachel; she has already met Alex, and as they embrace Alex assures her that Ingrid is strong. "Yes," she replies, "it runs in the family."
When the others leave them alone together, she asks Derek who would want to hurt his sister, and he tells her that it's actually him and the Legacy they're trying to hurt. Barbara is appalled that the kidnapper wants a "work of art" and wants to know if Derek will give it to them--or rather, will the Legacy allow him to give it to them? He says he hopes it won't be necessary, and that the Legacy will do the right thing. "Yes," she replies, "it always does." She's pleased to hear that Derek and his sister have been spending time together. "You are her strength," she assures him. "And she is mine," he answers. "We won't lose her, I promise." "I know," she says, "you and William will find a way; you always have." Surprised and angry to hear that Sloan is also there, he goes to find him.
Sloan is in the living room, shaking his head over the broken Mycenean artifact. Derek confronts him angrily. Everything is under control; Sloan has wasted a trip. "Not really," he replies calmly, as it's a long plane trip especially for a woman whose daughter is missing and a man whose "family" might be partially responsible. Barbara trusts him, he says; why can't Derek? He warns him again that he cannot allow his feelings to cloud his judgement as a precept. Derek reveals to Sloan that he believes Ingrid has been abducted by a rogue Legacy house, telling him of the Legacy ring seen by the witness to the abduction.
Through a process of elimination they determine that the one possible culprit is Angeline D'Arcy of the Montreal House. She joined the Legacy at the same time as Derek, and he reveals they were once "very close." She had helped him make up his mind to stay with the Legacy, but "eventually we had a...falling out." There was also something very familiar about the apparition that had appeared to Derek. Sloan needs more proof than Derek's feelings. He calls her; she uses the same phrase about time being a precious commodity that was used by the apparition. When Alex determines that the call had been re-routed and actually had come from Sonoma, Sloan is convinced. Leaving Alex to work on the chalice research and in case the kidnappers call, the team goes seeking Angeline.
In a dark, stone-walled room, a tied and blindfolded Ingrid is being taunted by Angeline. She knows Derek "very well," she taunts; Ingrid denies her. She mocks the nun's faith in God; money, beauty and power are the only things worth living for. When the nun professes her faith in God's will, Angeline slaps Ingrid and tells her if she dies it isn't because God wills it so but because she, Angeline, does. Angrily ordering the two robed figures to take Ingrid away, she sits in the vacated chair, twisting her Legacy ring.
Angeline's call has been traced to a disused winery. Rachel discovers the decomposing corpses of several Montreal house members, who appear to have literally rotted to death. Derek hears his name called and follows, the others right behind him. Suddenly Angeline appears to them in a doorway, robed in white. She refuses to return Ingrid and reveals she tricked them there. The Dark, she says, was always more interesting than the Light; she'd tried for years to convince herself she was learning more about it to better fight it. Instead, Derek says, "you were practicing the art of self-deception." "Wrong!" she cries; it was the art of self-revelation! Family, the Legacy, is nothing, the Dark side is all. "You can't imagine the power!" she cries. But the price is too high, William argues. "Good people killed; our trust betrayed." There is always a price, she says, and reveals--to the others' horror--her true, decomposing form. When William offers help, she refuses. Changing into the form of the young girl she reveals another deception. "Your family is your weakness, Derek. You'd do anything to save your sister. But now, you have condemned her." She fades away, and as they all realize she'd never been there with them at all they also realize it was to lure them away from the House so she could steal the chalice.
In the control room, Alex is studying the chalice when the lights suddenly go out. She hears a noise, then jumps when the cell phone rings. Derek tries to warn her of her danger, but before he can do so he hears her cry out, and the line goes dead. They arrive at the House to discover the lights still out, and Barbara in the control room trying to help Alex who's been knocked unconscious. She'd heard Alex scream and found her like this. Alex regains consciousness and Rachel carefully helps her to her feet and out of the room, as Sloan reveals that the chalice is gone. Derek berates himself for thinking so much about Ingrid he couldn't see Angeline's plans. William asks incredulously if he thinks his family is his weakness? "Do you think that was your weakness, that you were worried about your sister? That you were willing to risk yourself for your family? That's not your weakness, that's your strength." When Derek tries to apologize to his mother, she asks for what? "For placing your sister sister above everything else?" "I should have prevented this," he says. No one should have to make as many sacrifices as she has. "There's too much of your father in you," she tells him. "I knew as soon as you made your decision to join the Legacy you'd never be happy doing anything else. So don't tell me you're sorry for the choices you've made. Just find your sister before its too late."
In looking over all the information Alex got from the chalice before she was attacked, Nick recognizes the "decorative" jewels as a star pattern, and they narrow it to the pattern of the sky at mid-winter's night--that night. Angeline won't live until another solstice and needs to perform the ritual that night, and will use Ingrid for the sacrifice. The Aztecs used pyramids for their sacrifices; Angeline, they deduce, would seek the highest point in the area, which is Mt. Tamalpais.
On the top of the mountain, Angeline and her followers have created an altar surrounded by a stone circle and several lit braziers. Ingrid is in a white gown, gagged and tied to the altar, and Angeline explains the simple ceremony: Ingrid's blood drunk from the chalice will cleanse them and make them whole. In the meantime, Nick instructs Derek and Sloan to work their way closer while he tries to come around the back.
Angeline explains madly to Ingrid that it's the perfect solution, they'll both get what they want that night--Angeline will become immortal, while Ingrid will give her life helping someone else! As she is about to plunge the knife into Ingrid's heart, Derek calls out to her. Angeline thinks Derek has come to join her. Sloan urges her to stop what she's doing and to come back to the Legacy, and she scoffs at him. Come back to a pathetic mortal existence? She's tasted the power of the Other Side! When Derek wants to know if it was worth it, betraying him and attacking his family, she assures him that she did it because he's the one she wants! She tries to get him to "throw off the shackles of the Legacy" and join her, and when he cries out "Never!" she throws up a spell to keep him and Sloan back as she plunges the dagger into Ingrid's chest. With Derek crying out in despair, she collects Ingrid's blood into the chalice where it burns with a blue fire.
As she attempts to drink, Nick shoots and breaks her spell. Derek rushes forward and knocks the chalice from her hands, and she staggers back into the flames where she is consumed and disappears with a scream. Nick and Sloan restrain the two followers and Derek goes to his sister, who is not yet dead. Releasing her from her bonds he lifts her up. "Oh, my dear brother," she whispers, "I never lost faith...in you." She dies in his arms. "I was too late," he weeps. Sloan reminds him that the chalice has the power to heal. "Hurry," he urges, "before it's too late." Derek picks it up, and after removing the knife pours some of the remaining contents--Ingrid's own blood, changed mystically by the power of the chalice--onto her wound, which immediately heals. As Ingrid recovers conciousness she is embraced by her brother.
Derek's entry into his journal is voiced-over the image of him embracing his sister.