Artie is playing the piano at the B&B when Leena comes in and accuses him of eating the last of the oatmeal scotchies.
A helicopter transports the team, along with the comatose Artie. As they contemplate the dagger thrust into Artie's chest, the helicopter lands at Warehouse 13. They take Artie in while Claudia insists to Mrs. Frederic that for a moment, Artie was restored to normal. Mrs. Frederic warns the team that with the releasing of the Sweating Sickness, every person on Earth is now at risk.
16 Hours Until Mortalities
As reports start to filter in of people in Europe suffering from dizziness and excessive sweating, Mrs. Frederic briefs the team. Calder is in Atlanta with the CDC and has sent a warning that they're all at risk. Jane Lattimer arrives and warns them that the artifact plague is spreading more rapidly than anticipated. The incubation period is 24 hours, and they left Germany eight hours ago. Mrs. Frederic confirms that Artie is alive but catatonic, and they removed the dagger. She says that Claudia knows why there was no damage, because she instinctively stabbed Artie with the dagger. Claudia has realized that the dagger separates evil from good, and when she used it, she freed Artie from the Astrolabe's influence. Jane says that they have a theory to bring Artie back and takes Claudia and Steve with her.
Artie is in his bedroom and Jane tells Steve and Claudia that they need to reach Artie's subconscious and pull him back before it's too late and his mind shuts down.
Myka, Pete, and Mrs. Frederick check the background on the Black Orchid. The disease struck and then vanished, wiping out half of the afflicted each time. The Orchid turns to ash, releasing the plague, but they found it whole. Myka figures that there's an artifact that brings a flower back to life and they start looking for such an item in the records. Pete admits that he wishes Artie was there and wonders how any of them come back from the fact that the evil Artie killed Leena. Mrs. Frederic reminds the agents that Artie and Leena would both want them to keep the world safe. Myka finally locates a reference to the Count St. Germain, who brought flowers back to life, and they figure that he used an artifact.
Jane brings out a clock that belonged to Sigmund Freud and explains that it will them link their minds with Artie's subconscious and discover why he's trapped. Steve and Claudia immediately agree to help.
Pete finds a book on St. Germain written by Professor Bennett Sutton of Columbia University. Mrs. Frederic tells them to head to the university and talk to Sutton, and gives them Artie's bag for emergencies.
Claudia and Steve place their hands atop of Artie's and join hands, and find themselves in a mental representation of the warehouse. As they head to the office, Artie's "nerve center," a representation of Vanessa appears and tells them to leave. They hear a noise in the distance and Steve climbs up on the shelves to find out what it is. Vanessa tells Claudia that they need to leave and it's not safe, and that Artie doesn't want them there. Steve calls down to tell Claudia that the warehouse is shutting down as he dies.
At Columbia, Myka and Pete enter Sutton's office, covered in books and papers strewn everywhere. His assistant comes in and explains that Sutton's office always looks like that. She shoves aside the books, revealing Sutton passed out at his desk after a bout of drinking. The agents remind him that they have an appointment but Sutton isn't interested until he realizes how attractive Myka is. When Myka tries to get down to business, Sutton passes out. Pete slaps him awake and Sutton explains that St. Germain was a grifter who claimed he was a sorcerer. Marie Antoinette was an admirer of his ability to bring plants back to life, and St. Germain always wore a ring when performing the trick. However, Sutton is forced to stop his explanation when he throws up.
Claudia tries to tell Vanessa what is happening but the memory insists that Artie doesn't want them to die with him. Artie's bag appears but when Claudia opens it, she discovers that it's filled with snakes. Vanessa tells them to go and disappears but they continue toward the office.
After Sutton cleans up, he warns the agents that it won't be easy to find the ring. He explains that St. Germain's things were buried with him in the catacombs of Paris. Marie placed an impenetrable lock on the crypt and the catacombs are a maze. Myka points out that they have Boudin's map of the Paris catacombs, and Sutton is impressed. He offers to help them by providing the map's legend in return for some tax relief, and says that he can take them to the person who has it.
Steve and Claudia keep trying to get to the office but the warehouse shuts down ahead of them, cutting off their path. Claudia hesitates and complains that the warehouse keeps killing the people she loves. Even if they find a cure to the plague, nothing will bring back Leena. Steve insists that they have to keep fighting no matter what because evil is always relentless. Leena died risking her life to help Artie, and it was the fight that was important. Before they can move on, a representation of Mrs. Frederic appears and tosses a zookeeper's cap on the floor, trapping them in cocoons.
Vanessa is on the news warning about the spread of the plague across the planet.
7 Hours Until First Mortalities
In Paris, the trio arrives at a private home. Sutton explains that his rival, collector Charlotte Dupres, lives there. He warns the agents that Charlotte won't let them copy the legend, but admits that he made an anonymous call and lured her off to Barcelona. When Myka asks him for the truth, Sutton explains that he's pieced together that they need St. Germain's ring to heal the Black Orchid and stop the plague. The professor tells them to either help him break in so they can stop the plague, or not. The agents realize that they have to cooperate with him.
As Claudia and Steve try to get free, they realize that the darkness is getting closer. Steve spots a spear on the shelf above him and starts shaking, trying to knock it off. It finally falls onto the cap, destroying it and freeing them. They continue on and come face-to-face with a representation of McPherson. He shoots at them with a Tesla and they duck for cover.
The agents break into Charlotte's house and disable the alarm system. Myka realizes that Sutton is after something but he ducks her question and they begin their search.
McPherson stalks Steve and Claudia, explaining that he's there because Artie sees him as the embodiment of evil. Steve gets an idea and tells Claudia to go on ahead while he lures McPherson away. While she runs for the office, Steve tackles McPherson and knocks him into the darkness... and wakes up in the real world. He tells Jane that Claudia is still in Artie's subconscious.
Sutton leads them to Charlotte's study and they start searching while he goes into the next room. Myka starts to feel the effects of the Sweating Sickness but shrugs it off. She sees a painting and says that there's something they missed. Before she can explain, Charlotte leads Sutton in at gunpoint.
Claudia gets to the office but discovers that the door is locked. As the darkness closes in, Claudia screams Artie's name and the door opens on its own. She steps through and finds herself in the piano room at the B&B. Artie is playing and says that he doesn't want her there, and Claudia realizes that he's hiding. Leena comes in and accuses him of eating the last of the oatmeal scotchies.
Charlotte explains that the pandemic grounded her flight and says that the police are on their way. When Myka explains that they're not thieves, Charlotte points out that Sutton has stolen her gold coins, and he claims that he found them lying on the floor. Pete distracts Charlotte long enough for Myak to use her Tesla on the woman. When Sutton compliments them, Myka punches him unconscious.
Claudia warns Artie that if he stays then he'll be lost forever. He insists that things are perfect there and snaps at Claudia when she tells him he has to face reality. When she warns him that he'll disappear, Artie says that's what he wants. If he leaves with Claudia then he'll have to remember killing Leena. The representation of Leena takes in everything as Artie tries to continue playing but realizes that he can't.
The plague continues to sweep the world with thousands on their deathbeds.
1 Hour Until First Mortalities
When Sutton wakes up, Myka says that he lied to them. She points out that there were no portraits of St. Germain among his notes, and shows him a portrait that Charlotte has... which looks exactly like Sutton. As she makes her accusation, Myka collapses from the illness. Once she recovers consciousness, Sutton admits that he's St. Germain. An alchemist used the Philosopher's Stone to keep him from aging and then disappeared, and has kept his true nature hidden ever since. He tricked the agents into helping him recover his own belongings from Charlotte. St. Germain reveals that he found the legend, etched inside of a compass, and Myka reluctantly admits that she's impressed.
The trio goes into the catacombs while St. Germain explains that Marie eventually tried to have him beheaded. They arrive at the tomb and St. Germain explains that Marie provided the corpse of her servant Sebastian for the burial. There are several vases mounted on the wall and one of them is Chinese while the rest are Greek. Using the same artifact that they used at Charlotte's manor, the agents open the lock and go inside. The ring is on a stone hand at the far end of the chamber. As Pete snags the ring, St. Germain snags a diamond on the top of the tomb. Doing so sets off a series of dart shooters that fill the air with deadly blades. As they try to get out, St. Germain leaps in the way, taking a dart meant for Myka. They get him to cover and realize that the dart is poisoned. Myka thanks him for saving her life and St. Germain tells them to get out and use the ring. He dies and the agents place the ring on the Orchid.
Across the world, everyone infected with the plague is cured. The disease is drawn back to the Orchid and the agents realize that they've saved everyone... except for St. Germain.
Inside of Artie's mind, Artie, Claudia, and "Leena" watches as the darkness closes in on the B&B. Leena asks what Artie remembered of what he did, and Claudia tells her mentor that something made him do it. Artie says that the darkness is reality finding its way in, and Leena fades away. Claudia insists that some part of Artie wants to leave, and she'd do it again no matter how angry it made him. A door appears in the wall and Claudia figures that it's the way out. She tells Artie that he's not done fighting, even if he hasn't realized it, and tells him to go. When he refuses, Claudia shoves him through the doorway...
And Claudia and Artie both wake up. Claudia apologizes and Artie turns away, grief-stricken.
When Pete and Myka return, they discover that Artie has left his bed. Claudia walks away and Steve explains that Artie won't talk to them.
At the B&B, Artie is playing the piano when Mrs. Frederic comes to see him. She says that it wasn't him, but Artie points out that doesn't make a difference because he's the one who killed Leena. They both realize that they can't fix that, but Mrs. Frederic tells Artie that he can fix himself if he wants to. Artie says that he wants to and Mrs. Frederic promises that all of his friends will help him get through it. She asks him to play and Artie begins anew.
In the catacombs, Charlotte enters the tomb and talks of how she left Sebastian there hundreds of years ago. She then turns to the corner, but the only thing there is a bloody dart.