In St. Louis, Pete and Myka investigate a supposed gas explosion at a police station. Myka wants to get a brief vacation just to get out of South Dakota. They briefly examine the body, burned to a crisp, and meet Captain Powell. He explains a gas main leaked in the basement, causing the explosion, and abruptly leaves. They follow him past emergency generators used to power the station due to the damage and demand more specific answers, and he informs them one man is in critical and the other is in surgery. The agents go down into the basement and enter a cellar sealed up when the police station was built. Exploring, they find a metal door blown open and a chamber within. Inside is a desiccated corpse, manacled to a pipe. Checking his ID, they determine that the man was a Secret Service agent... equipped with a Warehouse electro-gun.
Pete and Myka call the Warehouse. Artie doesn't know who the agent is and the ID has crumbled to dust. Artie goes to the agent files while Claudia sees the incoming photos from the scene of the explosion. She reveals a device she's repurposed to project holograms of the photos. Artie is less than thrilled that she's been borrowing equipment without his permission. The device works and Claudia brings up a hologram of the corpse. He leaves her to reconstruct the charred parts and goes back to the file room.
At the police department, the agents review the tapes and Powell is still unhappy at their involvement. They finally get his attention when they explain that one person, Reggie Hinton, is missing. Powell puts out an alert while the agents wonder where Reggie is.
Reggie has escaped into the streets and warns his gang that there's something after all of them. Reggie and the others run off into something giving off an electrical discharge, killing them.
The agents arrive with Powell and determine Reggie and his friends were killed the same way, as if they were exposed to microwave energy. One of them has an unburned hand mark on his skin.
Claudia works to recreate the tattoo and Artie realizes the man was a Marine, narrowing down his search. Pete and Myka call and report no signs of a fire on the new set of corpses. Artie figures the deaths are deliberate, and they conclude someone found the artifact at the station and used it to settle an old score. Pete and Myka ask Powell for information from the head of the gang unit, but Powell says the sergeant, Clark, is out on leave.
Artie finally gets the agent's corpse back to the warehouse and examines it with a device that Claudia made. She starts assisting and manages to reconstruct the corpse's face. Artie goes through the files of Marines and realizes that it's Jack Seacourt, recruited in 1955 and last seen in Minneapolis. Artie goes to a special room and brings up the B&B room containing Seacourt's files, stored at the warehouse. Claudia finds a note saying Seacourt was going to meet a woman. Artie checks Seacourt's writing pad for imprints and reveals the last message he wrote, to Rebecca Sinclair in St. Louis.
Pete and Myka go to see an elderly Rebecca, who readily admits she knew Seacourt. They mention that Seacourt was dead and she wonders if it's connected to the explosion at the warehouse. She goes to get tea and cookies and then asks if there was anything strange about the body. As they talk, Myka gets a call about another body in the same condition and make a hasty exit. As they go, Rebecca wonders if other people have been electrocuted.
At the new crime scene, the only witness insists that the killer is a cop. Powell doesn't believe him but admits that Clark is the only officer unaccounted for. The agents ask for Clark's address. When they go there, they see electricity flowing around the door. They burst in and see Clark at the window, a mechanical lobster-like device attached to his back. He leaps out the windows, lands several floors below in the alleyway, and runs away. The agents chase after him and find him lying dead in another alleyway. The thing on his back is gone.
Pete and Myka send a photo of Clark to the warehouse and explain there was something fused to his back. Artie and Claudia examine Seacourt's back and discover there are similar marks. As Artie tries to narrow down the artifact from the description, Myka remembers that Rebecca asked about electrocutions when they didn't mention how the victims died. They go back to talk to Rebecca, who finally admits that she knows what Seacourt was involved with. They realize she's a Warehouse agent.
Artie locates the artifact in a book but he can't translate the writing. Meanwhile, Rebecca shows the agents photos of the unexplained deaths that occurred years ago. They had occurred after a museum display of 11th century pieces. Seacourt had an intuition and went off on his own, and Rebecca explains the Warehouse was Seacourt's first love. She went over the crime scenes and never found anything, and never went back to the warehouse, changing her last name and disappearing. Pete finds a manuscript referring to the “Hand of God” with a picture of man being struck by lightning. Artie calls in and reveals the artifact is the “Spine of the Saracen,” that was used to enhance Saracen warriors during the Crusades. They figure the item was sealed away and got released somehow. Artie is still trying to decipher the text and translates that it requires a lifetime commitment. However, they don't know where the artifact gets its power from. Pete and Myka figure it's at Clark's apartment and head back there.
Pee and Myka check out the alleyway and see a woman run out from a neighboring apartment. She's holding a gun and says she shot the man in the chest. The man comes out, bleeding from a chest wound and radiating electricity. The electro-gun has no effect, and the man begs them for help. He collapses, dead, and the woman explains that the man was her ex-husband. They turn the man over and discover the Spine is missing. They order the woman out and try to find the Spine, and Pete spots something moving in the bushes. It leaps for Myka and Pete shoves her out of the way. It attaches itself to him, shocking Myka unconscious when she tries to help him. Screaming in agony, Pete runs off. Powell and his men find Myka and she leaves to find Pete.
Myka contacts Artie, who explains that the Spine amplifies the host's life force and powers him up until the person runs out of energy. She tells Artie that it's on Pete. As they talk, Rebecca arrives to help Myka. Myka realizes it goes after whomever the host hates the most, and Seacourt sealed himself off rather then endanger anyone else. She figures Pete will do the same thing. Claudia speculates that electricity might be able to damage it. Powell tells Myka that his officers have spotted Pete heading back to the station... and the emergency generators.
Myka and Powell get to the station where Pete is attempting to hook the Spine up to the generator. Myka has Powell go back outside and tries to get through to Pete. He warns that he can't fight it much longer and has to end it by destroying himself and the Spine. Pete needs Myka to do it because he can't. Rebecca steps forward... and attaches the cables to the Spine. Myka tells him that she knows he'll come back. Pete tells Rebecca to throw the switch, and a huge charge of electricity shoots through him and the Spines. Pete collapses and the spine frees itself. Badly damaged, it crawls across the floor and Rebecca smashes it with a fire extinguisher. Myka goes to Pete and administers CPR. He revives and wants to know if Myka is okay.
Later, Pete and Myka returns to the warehouse and bring Rebecca with them. They introduce Rebecca to Artie and she gives him the shattered Spine. Artie suggests she might join back up but Rebecca refuses, saying she understands how the warehouse grabs people and doesn't let go. Now that she's completed Seacourt's mission, she's going home. Artie does offer to let her see one last thing: Seacourt's bedroom in storage. Claudia has found the engagement ring that Seacourt was going to give to Rebecca. Artie gives her a moment alone and Myka notes that Seacourt chose her over the warehouse after all. Rebecca tells Myka to quit her job now while she still has a life to live, and warns that Warehouse 13 is like the Spine: it'll use her up.