In Philadelphia, two students from the local engineering college go to a diner. A man wearing a baseball hat walks through the diner, goes out the back door, and chains it shut behind him. Inside, the two students, the cook, and the waitress look up in horror as a tentacled creature comes in the front door. The four frightened people try to run out the back but discover the door is locked. They turn on the creature and attack it with whatever weapons they can find. The police come in seconds later and stop them, and they realize that the creature was actually Joe, another engineering student.
Artie goes through Claudia's room looking for clues, and remembers how using the astrolabe would create an evil that would be with him forever. Leena comes to get him to meet with the others and they wonder what they're going to do to find Claudia. Artie tells them that the agent will be going to Philadelphia to investigate the attack after showing them that he received an artifact ping on Claudia's new pocket device. As they leave, Brother Adrian appears at the B&B's patio door and Artie invites him in.
Adrian is surprised that Artie seems to know him but introduces himself and explains that he's there on behalf of the Vatican' to obtain Artie's help recovering the missing Magellan's Astrolabe. It has vanished and the Templars believe that someone used it to rewind time 24 hours. The only way to stop it from unleashing a great evil is to have the original user employ the astrolabe a second time and undo what was undone the first time. Artie suggests that whoever used it was justified in stopping some great cataclysm, but Brother Adrian insists that the price is too great, gives Artie his card to call him, and leaves.
Claudia follows a Regent's agent to the hospital where Steve Jinx's corpse is being kept. As she watches from her car, she checks on the metronome artifact on the seat next to her.
In Philadelphia, Pete and Myka talk to the diner persons, who don't remember seeing anything that could be an artifact lying around. Pete makes a sketch of the creature from the witness descriptions and Myka admits that she doesn't like creatures with tentacles. They figure that the artifact was something that wasn't there when the cops arrived since they weren't affected, and the agents close down the diner to conduct a search.
At a dental office elsewhere in the city, an accountant comes in to get his teeth checked. The staff and patients see him as a tentacled creature and knock him back out the window where he falls to his death. The man with the baseball cap is among those who gather on the sidewalk to see the accident.
Claudia, dressed as an executive enters the hospital and manages to bluff her way past the front desk guard. She then switches to a nurse's uniform and goes to the morgue, and another guard demands to see her badge. The badge is rigged with a taser charge, stunning the man, but the desk guard comes in to check on her. Claudia prepares to use her Tesla on him but Artie arrives just in time and hauls her out.
Pete and Myka get word of the new incident and check the dental office, but fail to find a connection between the diner and the dentist's office. Myka calls Leena and has her check police scanners to see if they can find reports of any similar incidents.
Claudia insists on bringing Steve back to life, even though Artie warns that they can't use artifacts for their own selfish needs. He asks her if Steve would want her to risk everything to bring him back and Claudia asks her mentor if he would use an artifact to rectify a mistake. Regent Jane Lattimer arrives and Artie tries to cover for Claudia, but Jane says that Claudia has permission to use the metronome to bring Steve back. Artie warns against it but can't explain why without revealing his use of the astrolabe. As Artie leaves, Jane asks Claudia if she's sure. When Claudia says that she is, Jane says that they have to make arrangements to bring Steve back.
In Philadelphia, Robin is returning home from shopping when the man with the baseball hat approaches her and offers her an old-fashioned silver key which he thinks she lost. Robin says that it isn't here and the man leaves with the key. However, when Robin goes inside, her husband Jimmy sees her as a tentacled creature and panics. Leena hears about the incident on the scanner and calls in Pete and Myka. When they arrive, they talk to Jimmy, who explains that he locked the creature in a closet. Pete opens the door and Jimmy is the only one to see Robin as a creature. He attacks her and the agents restrain him.
Jane takes Claudia to the B&B where Steve's corpse is being kept in Claudia's room. When Claudia wonders if Steve will come back changed, Jane assures her that he'll be fine and they begin. Claudia places one hand on the metronome and one hand on Steve's chest, and Jane tells her to focus so she can bring Steve back.
Artie arranges to meet with Adrian at the local detail and claims he needs more information about the evil the astrolabe can cause so he can find it. Brother Adrian explains that the evil is unique to each user, and will cut through the user's heart like a dagger.
Steve draws a breath, startling Claudia, and Jane tells her to focus or she'll die as well.
Artie asks if the evil Adrian describes could be triggered by a resurrection and the brother admits that it's within the realm of possibilities.
Claudia finds herself in a white room with Steve, who is facing off into the distance. Jane tells Claudia to concentrate and get Steve to come to her, but Steve can't seem to hear Claudia. He finally turns to face her and comes to life as Claudia hugs him.
Brother Adrian tells Artie that knowing the evil won't help recover the artifact, but finally explains that Robespierre used the astrolabe. Doing so unleashed the French Revolution and the Reign of Terror. Adrian insists that the only way to stop the evil is to reverse the original temporal alteration.
In Philadelphia, the police arrive and the agents tell them that Jimmy was hallucinating due to bad mushrooms. They talk to Robin, who describes the man with the baseball cap and the silver key. Meanwhile, Pete goes over the sketches of the creatures taken from the eyewitness descriptions and realizes that they look like the monsters created by writer H.P. Lovecraft for his Cthulhu mythos. The agents call Leena, who confirms that Lovecraft suffered from night terrors which he blamed on an artifact called the Key to the Gate of Dreams. Pete and Myka realize that the source of the hallucinations is the victim, not the witnesses, and they go to the apartment of the engineering student, Joe. Pete discovers that Joe went to a recent Philadelphia vs. Cincinnati game where a riot broke out, and Myka remembers the name of Theresa Hicks, the one person who died there.
At the B&B, Claudia avoids telling Steve about his death but assures him that he was a hero, finishing off Sykes and Marcus Diamond. Steve begins to grow suspicious and uses his ability to tell that Claudia is lying to him. He hears the metronome ticking from inside its case and runs off when he realizes that Claudia resurrected him.
Pete and Myka got to the stadium and review the security footage of the riot. They spot all three victims and discover that they all ignored Theresa, letting her be trampled to death. Theresa's fiancé Ron Hadsell was there but couldn't save her, and they realize that Ron is the man with the baseball cap. The agents figure that Ron decided that his three victims were all monsters, found Lovecraft's key, and made them appear as monsters. When they go over the footage again, Pete and Myka spot a driver who parked his car in front of the ambulance that was taking Theresa to the hospital. Pete goes to help the driver, Jeff Green, while Myka tries to find Ron at his apartment.
Claudia finds Steve out on the B&B's patio and he wonders how long he was dead. She sheepishly admits that it was for three days and refuses to apologize for brining him back, and insists that she'd do it again if she has to. Steve warns her that he doesn't know if he feels or what he feels, and that it'll take some time to get used to his new circumstances.
Myka breaks into Ron's apartment and finds photos of him and Theresa today. He also has a workshop where he makes models of Lovecraft's monsters. Meanwhile, Pete arrives at the driver's house but no one answers the door. Myka calls her partner and tells him that Ron is the guy they're after, just as Ron arrives at Jeff's house. He sees Pee and runs into a nearby fitness center, and Pete goes in after him. Ron uses the key on him and, when Pete says that he's there to help, says there's nothing they can do if they can't bring Theresa back. The people in the fitness center see Pete as a monster as Ron calls them over, and Pete tries to call Myka but she can only hear a roar.
Following the commotion, Myka enters the fitness center and holds off the patrons even though she's having trouble coping with Pete's new appearance. When she realizes that Ron is responsible, she gives her Tesla to Pete and chases after Ron. She captures him and neutralizes the key just in time as the patrons disarm Pete and move in for the kill.
Later, the police arrive to arrest Ron. He insists that he tried to go to the police to get justice for Theresa, but they said it was an accident. When Pete wonders why he didn't just shoot his four targets, Ron admits that he couldn't bring himself to use a gun. He had rumors of the key at horror conventions, found it, and used it to show their victims what they truly were: monsters. As the police take Ron away, Pete has no sympathy for him but Myka admits that she can understand how grief can drive people to do something they know is wrong.
When Claudia returns to the warehouse, she finds Adwin and Jane waiting for her. She realizes that Jane disobeyed orders to bring Steve back, and Pete's mother insists that they owed Steve since he died in their service. Adwin warns that there are consequences and that Steve is linked to the Regents and the warehouse as long as he's dependent on the metronome. The Regents have no choice but to keep Steve under lifetime supervision, and eliminate him if they discover the metronome has a downside.
Back at the B&B, the others are reunited with Steve. Claudia arrives and Artie, knowing that Adwin is there, realizes what happened. She wonders if the two of them are okay given her earlier actions and Artie assures her that they're fine. As Claudia goes over to Steve, Artie gets a ping and discovers that someone has reported a dagger: the same dagger he saw Claudia use to kill him in his dreams. Pete notices Artie's look of shock and Artie assures him that he's okay, but Pete isn't convinced.