Nothing like the 'burbs to inspire a murderous spike, and the gated community in Marlon, Ohio, is feeling that bump when a district attorney is poisoned and falls down dead on his lawn. Pete is feeling some kinda weird spike, too, after the doctor performing his physical tells him his testosterone levels are low. Could there be a worse prognosis for someone with Pete's love of heroism and burliness? Soon after they arrive at the crime scene, another strange occurrence arises - a young man and his older "business associate" get stuck together, as in, their skin grafts onto the other and makes them look like Siamese twins.
Steve has elected to stay at the warehouse to clean the goo depository, but his ulterior motive is to unload some worries on the new resident therapist. She gives him some insight by sharing her own story, and they bond over being alone in the world except for their Warehouse comrades, who are family aplenty. And soon after, Steve and Abigail become the research assistants for the two teams, looking up sin artifacts for Myka and Pete, who have discovered a third victim who spontaneously ignites, then psychic artifacts for Artie and Claudia, who are trying to save a 15-year-old street kid in New York who keeps pouring out genius-level math equations. After the trance that allows the math to flow, the kid, Nick, goes into massive seizures.
Jinks and Abigail are a ton of help to Myka and Pete, telling them that three as-yet undiscovered artifacts are known to have been created in the destruction of Sodom and Gomorrah. But the biggest fan of rules succumbs, too, telling the agents through a coughing fit of orange gas that when he was in Kuwait as a U.S. colonel, he had to gas an entire village, and believes he is now being punished for that. When Myka starts brainstorming on salt-related artifacts, she realizes that the artifact may not be your run-of-the-mill urn or clock, but may be salt, itself. She connects this possibility to a town busybody named Janice Malloy, who recently had a butting of heads with the town board of supervisors over erecting a bust of her late husband, the founder of the town - and also makes a mean chocolate cookie, dusted with salt.
She calls this revelation over to Pete, who, having tasted the cookie of good and evil, is the next victim. His body is thrown by an unseen force out of a second-story window, and when he lands, his legs are hideously twisted. Myka rushes to Janice's house where another board member is about to eat the cookies, and Myka has a violent showdown with Janice where she barely manages to bag the artifact - a sheath of salt that took the form of a condemned man's face. She finds Pete and sees that his legs are broken, even though the artifact is bagged. Just then the colonel, in full health, returns from the hospital. Myka orders him to call an ambulance, then wracks her brain to deduce how the colonel recovered. She realizes he confessed his sin, and slowly gets Pete to reveal that, while he was still drinking heavily, he crashed his car. He walked away, but his buddy in the passenger seat broke both his legs. As Pete sobs his confession, his legs return to normal, and he thanks Myka for being there for him in so many ways.
On returning to South Dakota, Pete and Myka discover they have a new roommate - it's Nick, the victim of the artifact in New York. During his seizures, he was able to describe what he saw, allowing Artie and Claudia to pinpoint the user of the artifact as a "quant," a math specialist at an accounting firm. After the artifact (Orville Wright's goggles) have been snagged and bagged, Claudia realizes that Nick has nowhere to go. As a former street kid herself, she wants to pay forward what Artie did for her and give Nick a safe place for long enough to shape up his life. He agrees, and is happy to enter the B&B to the smell of lasagna, cooked by Jinks, himself.
But the ending isn't a happy one, for it doesn't end there. Nick texts Charlotte Dupres and tell her their plan is working, and Myka, after her yearly physical, hears the doctor tell her she has ovarian cancer. She is floored by the news, too scared to share it with anyone.