After discovering that the main suspect for providing the C4 to the bomber has been visited by Ambo 61 multiple times, Voight and Antonio ask Gabby and Sylvie to go back to the house and serve as a distraction while Adam breaks in and clones the suspect's laptop. Despite Matt and Boden's reservations, the women insist on helping. Things get a little dicey when the suspect's brother shows up in the middle of their "wellness check," but Gabby covers, and Adam gets the information the intelligence team needs.
Back at the house, Cruz is drastically over-reacting to Sylvie's decision to help intelligence. Some of his reaction is because of his unrequited love for his roommate and some of it is because of his brother's experience working with Intelligence. It doesn't help that Antonio is one of the cops asking for help. Sylvie spends a good amount of shift hiding from her roommate, but Cruz eventually finds her and tries to insist he's only worried as a friend.
Squad gets called out to another bombing, which all but confirms Intelligence's second suspect as the bomber. Kelly and Boden go through past calls to make the final connections, finding the locations where the IEDs were tested. By tracing down the owner of the property, they're able to locate an email between the provider of the explosives and the suspect, which leads to his next target.
After figuring out that he's trying to hit a metro station, Casey and Kelly are able to stop the bomber and save the day. After drinks to celebrate at Molly's, Antonio and Sylvie hook up in his car. Stella reveals that HazMat Zach broke up with her, and she and Kelly stay in for a night snuggled on the couch watching old movies.