Pete and Myka travel to South Bend, IN, to investigate a report about a toy collector, Barry Byck, who has been growing. He explains that he's grown three inches in the next week, but recently his joints have started hurting. As the agents look around the apartment, they wonder if Barry is imagining things and if Artie sent them on a wild goose chase to get them out of the warehouse. However, when they check back on Barry, they discover that he has grown even further. They call Leena on the Farnesworth and she tells them that she has received more reports of growth spurts. The agents check on another victim, Lisa Bernardo, and her limbs start growing out of control as she cooks a meal for the church where she works.
As the EMTs take Lisa away, the agents get hold of Artie, who is distracted working on the warehouse's theft detection system. They have the name of someone else who has reported a growth spurt, lawyer, Anthony Seklir, and try to work out what artifact might be responsible. Artie signs off no them but is startled when Claudia and Steve come in. They show him the black diamond that they found and Claudia demands to know what is going on. Artie insists that he's trying to protect them but the two agents insist that they can handle it and Artie apologizes for his rudeness.
When Pete and Myka go to Seklir's office, they find him eating a Mexican lunch with hot sauce. He complains about heartburn and takes some pills with a brand name of Reduxid and Myka remembers that Barry was also taking heartburn pills.
At Moorpark Pharmaceuticals, Deb Stanley reports to the owner, her boss Gil, that they're getting reports of people who are growing. She suspects that their medicine may be involved and asks for permission to check it out, insisting that it could be a major breakthrough. Gil considers and then agrees.
Pete and Myka go back to Barry's apartment and discover that his body is starting to rip itself apart because of the growth spurts. They take him to the hospital with the other victims and the doctor admits that they will all be dead within two days. All of them received Reduxid from the same doctor, Selden, and the agents go to his doctor's office. Deb is there, waiting outside, and becomes interested when she sees them. Pete identifies himself as a Secret Service agent and tries to intimidate her and the agents talk to Selden in his office. He confirms that he only treated two of the victims, as Deb barges in and explains that her company made Reduxid. The agents point out that her drug may be responsible for the growth spurts and Deb suggests that they work together to figure out what is going on. She has the medical records but the patient names are coded for confidentiality purposes. Deb offers to help contact the doctors who aren't covered by confidentiality and Pete goes with her while Myka checks on the background of the four victims to find a common denominator.
Artie tells Claudia and Steve about Brother Adrian without explaining why the Brotherhood is interested in him. Claudia admits that she already identified him when she checked the Internet for information on black diamonds. They figure that Adrian is using an artifact to break into the warehouse undetected, and Artie gives them the cell phone number that Adrian gave him so they can run a trace. As they leave, Artie remembers Adrian's warning that anybody he tells about what happened will be in great danger.
Myka calls Pete from the field and tells him that she hasn't found out anything connecting the victims. She suggests that he charm Deb into helping them and hangs up, and Pete asks Deb about how she got into pharmaceuticals. She explains that her father was a doctor but that she wanted to get into a field where she could still make discoveries. A little later, they end up in bed together at Pete's hotel room. When Myka arrives, Deb hides in the closet but Myka soon Pete has been sleeping with the pharmaceutical rep. She tells her partner that the newest victim was a Christian Scientist who wasn't taking any drugs. Myka has the Golden Spike from the Transcontinental Railroad, thanks to Artie sending it. They figure that since it brings things together, they can use it to at least temporarily stop the growth spurts. Once she leaves, Myka emerges from hiding and they both agree that they had a good time and that it wasn't anything more. Despite that, Pete is somewhat disappointed that Deb doesn't think it's anything more than that. He tells her that Moorpark is off the hook and there's nothing else for her to do. Deb still wants to help but Pete tells her that she can't and promises to call her later.
The agents get a report on the next victim, Karl Irving, and get to his house as he staggers out. As the EMTs arrive, Pete distracts them while Myka uses the spike to help Karl. Pete slips away once he sees that Myka has succeeded... unaware that Deb has been watching from nearby. They go to the hospital and treat the other victims with the spike, slowing down their growth. Deb, who has secretly watched the entire thing, calls Gil and tells him that she's stumbled across a group that uses items with revolutionary medical applications. Gil tells her to keep investigating and promises that they will only use anything she brings back if it's proven safe. When Karl's fiancee arrives to check on him, Deb offers to take her up.
Steve and Artie rewire the detection system and discover that Harriet Tubman's thimble is missing. They go to the shelves and discover that Adrian has left a black diamond in place of the stolen artifact. Claudia returns to tell them that she's tracked Adrian's cell phone. They drive to the GPS location, a manor outside of Sturgis, and split up to search the house. Claudia and Steve go in the front and call Adrian's phone, and hear it ring from a nearby desk. They look up and see Adrian on the second floor balcony, carrying a wooden plank with Roman lettering on him. He runs off and they start searching the house.
In South Bend, the agents go over Deb's records trying to find a connection between the victims. They discover that each one started taking the medicine at about the same time and Myka discovers that Barry took a cooking at Le Cordon Bend. Karl was the teacher and specialized in spicy food, causing all of the heartburn, and the other victims were students. Karl uses antique cooking utensils at his school and the agents figure that one of them is an artifact. However, when they get to the they discover that the building has been cleaned out and Pete realizes who is responsible.
Deb calls Gil and tells him that she's cleaned out the school and sent the cooking utensils to their R&D lab for analysis. However, she has one more stop to make.
At the B&B, Leena identifies the plank as the Threshold of Limentinus, the Roman God of entryways, and confirms that it can create an opening in any wall. She calls to tell Artie and he continues his search. Meanwhile, Leena hears someone knocking at the door. When she opens it, she finds Deb on her doorstep. The pharmaceutical rep says that she knows Pete lives there and she has a lot of questions for Leena.
Myka confirms that Moorpark Pharmaceutical bought the school and sent the utensils to their R&D lab in Minneapolis. Leena calls on the Farnesworth to tell them that Deb is at the B&B. Myka figures that Pete screwed up but he insists that he got a good vibe off of Deb. They try to work out what to tell her and Myka warns her partner that they can't tell Deb the truth. She heads off for Minneapolis while Pete goes back to the B&B to deal with Deb. When he gets there, Deb admits that she traced his travel records. She also knows about the various medically-related incidents that the agents have been involved in over the last few years. Pete tells Deb that she needs to get out before his bosses decide to do something about her. However, Deb tells him that people know where she is and she's not afraid.
Gil calls Senator Don Stafford in Washington and makes a substantial donation to make sure that the government doesn't impound the artifacts as some department in the government is threatening to do.
Steve and Claudia go down into the cellar and spot Artie, but Claudia realizes that "Artie" is wearing Tubman's thimble and that it's Adrian using the thimble to disguise himself. They fire at him and Adrian shoots back and then runs off into the darkness without the plank. Artie calls them and they tell him what's going on just as Adrian finds Artie and removes the thimble.
Pete tries to convince Deb that all of the stories that she has heard are just urban folklores. Regent Adwin Kosan arrives and talks to Pete privately. He warns that Senator Stafford is now calling the White House about the warehouse on behalf of Moorpark, and that Moorpark is pressuring Stafford to give them access to the artifacts. Mrs. Frederic is in Washington trying to shut down the probe but Kosan isn't sure that she'll succeed. Rather than dispose of Moorpark, Deb, and Stafford, Kosan first asks Pete what kind of vibes he's getting from Deb. The agent says that she's smart and basically good, and the Kosan tell him to show Deb the warehouse.
Myka arrives in Minneapolis and sneaks into the Moorpark R&D lab. One of the technicians is growing uncontrollably and the other technician admits that he doesn't know which of the many utensils his friend was touching.
Pete takes Deb to the warehouse and tells her about its history. As they go through the shelves, Deb is eager to start using the artifacts to cure disease. Pete warns that all of the artifacts have a magical downside but Deb points out that everything in life has a downside and magic is just science they don't understand yet. The agent realizes that it's personal for her and Deb explains that her father died of Parkinson's. Pete shows her an artifact that could have cured him, but it would have given the disease to someone else. He asks Deb if she can guarantee that Gil and the people who work with him will always do the right thing and asks if Deb is willing to take that risk.
Myka and the lab tech go through the piles of utensils and the agent finally finds a marble bowl made from a shard of the Colossus of Rhodes. She neutralizes it and the afflicted technician stops growing. Before anyone can question her further, Myka slips away with the artifact.
Artie tries to work with Adrian, asking him what evil will be unleashed so that he can stop it rather than undo the astrolabe. Adrian refuses, saying that he has plenty of other artifacts that he can use to strike at Artie. When Artie warns the brother that undoing the astrolabe will kill Adrian, Adrian assures him that he's willing to make any sacrifice to eradicate evil.
Claudia and Steve find a chamber where the plan is leaning against the wall. There's a crude barricade of furniture and they start moving the items... unaware that there's a tripwire on the other side.
Adrian tells Artie that until he undoes the astrolabe's effect, he will continue to destroy everything in his life. Artie realizes that Adrian has set a trap and yells over the earbud to Steve and Claudia. They move the furniture and there's an explosion. Artie goes to help them while Adrian slips away. However, the younger agents are fine and tell Artie that they figured it was a trap and triggered the bomb to make Adrian think they died. When Artie admits that he's glad Claudia isn't buried alive again, she asks what he means but he refuses to explain.
Gil brings Stafford to the warehouse after Deb gives him directions. One of the Regents, Mr. Keeler, escorts them in and Gil is surprised to discover that it's a government storage depot containing old toys. Stafford suggests that Gil should fire his employee for wasting their time.
Later at the warehouse, Pete tells Deb about Myka recovering the bowl. She figures that she's out of a job and admits that she kept the Hippocratic Oath in mind to do no harm. Deb believed that keeping the warehouse a secret would do that. Kosan comes in and asks to talk to Deb alone. Once Pete leaves, Kosan thanks Deb for her help and explains that he is one of the Regents that oversee the warehouse. He suggests that Deb might be suitable to become a Regent given her proven loyalty and she leaps at the opportunity.
When Artie, Steve, and Claudia return to the B&B, Artie thanks them for their help but says that he has to end their involvement before they come to harm. Claudia agrees immediately but Steve is sure that she doesn't mean it. Artie then secretly meets with Helena as she comes in the back way. She tells him that she found the knife but then asks Artie why he vouched for her with the Regents. He tries to put her off but Helena asks how he knew about the artifact bomb in Sykes' wheelchair. She then accuses him of using time travel to have come back from the future where he gained knowledge of what was happening the present. Artie tells Helena that she can't tell anyone what she has deduced, but she tells him that she has already spoken with Mrs. Frederic and they've realized that Artie used the astrolabe.