In South Bend, IN, Pete and Myka go to the apartment of a collector, Barry Byck, who explains that he's grown three inches since he updated his dating profile. He complained when things got painful and his joints started aching. The agents discuss the situation privately and wonder if Artie just wanted them out of the warehouse on a wild goose chase. However, when they turn back to Barry, they discover that he is growing as they watch. They contact Leena, who sends them the name of Lisa Bernardo, who has also reported a sudden growth spurt while cooking at a church. As they check on Lisa and Leena calls them with another report, the woman screams in pain as her limbs starts stretching.
As the EMTs take Lisa away, the agents contact Artie and tell him that there have been four cases. Artie is busy in the shelves and barely paying attention as the agents tell him that they have to contact one more person, Anthony Seklir. They try to work out which artifact might be responsible but Artie is more interested in his wiring project. Once they sign off, Steve and Claudia come in, startling Artie. They show him the black diamond that they found and Claudia points out that he's working on the artifact detection system. Artie tells them that he's not telling them because he's protecting them, but the agents insist that they don't need protecting.
Pete and Myka meet with Seklir, who is having Mexican for lunch. He takes heartburn pills and Myka remembers that Barry was taking heart medication.
At Moorpark Pharmaceuticals, Deb Stanley reports to her boss Gil Moorpark that they're getting reports of people taking their medicine who are growing. Gil insists that there's nothing to it but Deb suggests that it could be a major breakthrough, and he sends her to check it out.
Pete and Myka return to Barry's apartment and discover him growing painfully out of control. They get him to the hospital with the others and the doctors confirm that they'll be dead in two days as their bodies tear themselves apart. The records show that they all received a medication, Reduxid, from Dr. Selden. They go to Selden's office and ask for the doctor, and Deb interrupts them from where she's waiting. Pete identifies himself as a Secret Service agent and they talk to Selden, who says that he only treated two of them. Deb pokes her head in and says that she's with Moorpark and they make Reduxid. The agents tell her that their drug is putting people in critical condition and Deb explains that it's only happening in South Bend. They ask her for the company records and Deb suggests that they work together. She gives them the coded files and admits that she doesn't have the patient names because of confidentiality issues. However, Deb offers to call the doctors and Myka checks on the four victims they know while Pete goes with Deb.
Artie tells the agents about Brother Adrian and Claudia says that she already knows about him from checking the Internet when she looked up the black diamonds. All Artie will say is that Adrian has a grudge against him because he won't do something, but refuses to say what it is. He snaps at them and apologizes, and they figure that Adrian is using an artifact to get in. As Claudia and Steve leave to trace Adrian's cell phone, Artie remembers Adrian in the original timeline warning him that anybody he warns will be in danger.
Myka calls Pete and says that she hasn't found anything, and tells him to keep working with Deb and charm her into helping them. Once he hangs up, Pete turns on the charm and Deb says that her father was a doctor but she prefers working in a field that is still discovering things.
Later that afternoon, Pete and Deb end up in bed at Pete's hotel room. Myka arrives and Deb hides while a semi-naked Pete lets Myka in. She says that there's a new victim and that he was a Christian Scientist who wasn't taking drugs. Artie has sent the Transcontinental Gold Spike, which brings things together and thinks can cure the victims temporarily. She realizes that Pete slept with Deb and he assures her that she's unarmed, but Myka is not amused. Once she leaves, Deb emerges from hiding and they both agree that they had a good time. Pete tells her that the last victim didn't take her pill and there's nothing else for her to check out since her company is in the clear. However, Deb says that she wants to help regardless. Pete tells her that she can't and promises to call.
The agents arrive at the new victim's home as he staggers out as the EMTs arrive. Pete distracts the EMTs while Myka uses the spike on the victim. Once he stabilizes, Pete confirms that Myka is clear and tells the EMTs to check on their patient... unaware that Deb followed him and saw the entire thing.
The agents go to the hospital to treat the next victim with the spike. Meanwhile, Deb follows them and calls Gil to tell him that she's following two agents that use objects with medical applications. Gil assures her that they'll pursue any product as long as it doesn't have adverse effects and congratulates her. The fiancée of one of the victims, Karl Irving, comes in and Deb offers to escort her up.
Steve and Artie finish rewiring the detection system and they discover that Harriet Tubman's Thimble is missing. They check it out and find another black diamond in place of the thimble. Claudia has tracked Adrian's cell phone number from when he called Artie and the trail leads to a manor outside of Sturgis. The trio go there and Claudia and Steve go in the front while Artie circles around the back. Claudia calls Adrian's phone and they hear it ring from inside a desk. Adrian walks past upstairs, carrying a wooden plank with Roman lettering on it, but they lose him and start searching.
The agents try to work out what the victims have in common besides the drug and go over Deb's records. Each one had a spike in their heartburn on the same night and got taller a few days later. They check Barry's receipts and discover that he took a cooking class at Le Cordon Bend. The others took the same cooking class and Karl, the teacher, specializes in spicy food and uses antique cooking utensils. However, when the agents get there the next morning, they discover that it's been cleaned out. Pete realizes who is responsible.
Deb is driving back to Moorpark and calls Gil, assuring him that she cleaned out the place and had the artifacts sent to the lab for analysis. She then tells her boss that she has one more stop to make.
Leena checks the database and confirms for Artie that the plank is the Threshold of Limentinus, which can create an opening in any wall. Artie keeps searching and hears someone moving up ahead. As hangs up However, Leena hears a knock at the door and goes to answer it. It's Deb, who says that she knows Pete lives there and has a lot of questions.
Myka confirms that Moorpark bought the entire school and sent it to R&D in Minneapolis. Leena calls to tell them that Deb is there and Pete tells Myka that he got a good vibe off of her. He plans to tell her that people will die unless she gives back what she took, but Myka points out that they can't tell her the truth. She tells Pete to go back and clean things up while she goes to Minneapolis and recovers the artifact.
Pete goes to the B&B and Deb explains that she traced their travel records. She has records on them of several strange incidents that they were involved with, and Pete tells her that she needs to get out before his bosses come after her. Deb isn't impressed and says that people know where they are.
Gil checks with Senator Don Stafford and gets him to release the artifacts after Moorpark makes a substantial donation to his fundraising committee.
Steve and Claudia find Artie in the cellar, but they quickly realizes it's Adrian using the thimble to appear as Artie. Adrian returns fire and runs off, and the agents realize that he didn't have the plank. Artie calls them and they warn him that Adrian looks like him. Adrian comes out and removes the thimble as Artie aims his Tesla at him.
Pete insists that whatever Deb thinks, she's wrong, and the rumors are just urban folklore. Kosan arrives and asks for a word with Pete, and explains that Senator Stafford is now calling the White House about the warehouse. The regent warns Pete that Moorpark is pressuring the senator to give them access and Mrs. Frederic may not be able to shut down the inquiry. Kosan says that they have a plan but it is messy and borders on treason, and says that they have an alternative. However, it relies on Pete. Kosan asks Pete what his vibes say about Deb and Pete says that she's smart and basically good. The regent then says they need to consider another option: show Deb the warehouse.
Myka sneaks into the R&D lab and finds one of the technicians growing out of control. Unfortunately, the lab is filled with all of the artifacts from the cooking school.
Pete shows Deb around the warehouse and tells her the history of the Warehouses. Deb is eager to use the artifacts to cure diseases but Pete explains that they all have downsides. She points out that everything has a downside and that everything is magic until they understand it. She's eager to make new discoveries and finally admits that it's important to her because her father had Parkinson's. Pete considers what she's said and then shows her the artifacts that could have cured her father... but they all have downsides. He asks if Gil will always do the right thing or will use the artifacts as weapons. Pete wonders if she's willing to take that risk.
Myka and the other lab tech try to narrow down the last thing that the suffering technician touched. The agent finds a marble bowl from Rhodes and neutralizes it, and the technician revers to normal. Myka then takes off with the artifact before anyone can stop her.
Artie asks Adrian what the evil is in the hopes that they can stop it, but Adrian says that he has plenty of artifacts and will continue his assault on Artie's life. When Artie points out that restoring the original timeline will kill Adrian, the brother says that he's willing to sacrifice his life to eradicate evil.
Claudia and Steve arrive in the cellar and spot the Threshold behind a barricade. They start moving the items, unaware that there is a tripwire.
Adrian tells Artie that he will continue erasing every good deed he's done and isolating him from everyone he cares about. Artie realizes that it's a trap and calls to tell Claudia and Steve not to move. As they go in, there's an explosion and Adrian slips away while Artie is distracted. Artie runs to the cellar and discovers that Claudia and Steve are okay. They explain that they found the trap and triggered it on purpose. When Claudia admits that he's relieved they're not buried alive again, Claudia wonders what he means while Steve recovers the Threshold.
Gil brings Stafford to the warehouse based on Deb's directions and a regent escorts them into... Storage Space Six. It's filled with toys and the senator suggests that Gil fire his associates.
At the warehouse, Pete tells Deb about the bowl and she figures that she's been fired by now. He asks what changed her mind and Deb says that the best way to avoid harm is to keep the warehouse a secret. Kosan comes out and asks to talk to Deb alone, and thanks her for her help. He explains that he's with the Regents and they oversee the warehouse. Kosan suggests that she may be suitable to become a Regent and Deb leaps at the opportunity.
Artie, Claudia, and Steve return to the B&B and Artie admits that he needed their help. But he still can't tell them everything without putting them in danger so he's ending their involvement. Claudia immediately agrees but as they leave, she assures Steve that they're not done. Meanwhile, Artie greets Helena as she comes in via the patio. She tells him that she's found the knife but first she wants to know why Artie vouched for her so enthusiastically. Helena wonders how he knew that Sykes had a bomb in his wheelchair and is sure that he came back from the future and knew what would happen. Artie says that she can't tell anyone what she suspects, but Helena admits that she already told Mrs. Frederic that he must have used Magellan's Astrolabe.