The squad responds to a hydrochloric acid spill, a daunting task to contain since the spill grows at a faster rate than they can neutralize. Sensing an opportunity, Dawson goes off-book and commandeers a nearby dump truck, pouring the dirt over the spill. Although this contains the spill, she never cleared her actions with Casey and a battalion chief happens to stop by right as she exits the truck. Not exactly good timing for everything.

In private, Boden warns that another incident like that could spell trouble for both Dawson’s candidacy and Casey’s reputation, a sentiment that Casey echoes to his fiancée. This hits Dawson hard and initiates a rift between her and Casey. She attempts to approach him several times about the incident in an effort to quell the tension, but each time Casey meets her with icy rejection.

Another relationship appears on the rocks when Brittany finally opens up to Severide about her past. In a tearful confession, she reveals that her sister died in a car accident – and that Brittany was at the wheel. Unable to face her family, Brittany fled town and ended up in Las Vegas. Severide bonds with her over their shared sense of guilt and the next time Brittany’s family calls her, she answers. Her reconnection spurs another conversation with Severide at Molly’s… and they agree to end the marriage, realizing that they provided an escape for each other. Brittany needs to return home. Severide understands and, at the train station, they once again confess their love. In an emotional goodbye, Severide watches Brittany leave. Okay so that lasted…two maybe three weeks. Where did you guess?

Meanwhile, Mills and Brett respond to a secondary drowning victim who goes into cardiac arrest en route to Chicago Med. Despite a serious effort from Mills, the victim passes away at the hospital. Turns out the deceased is the son of Papa Lullo, a major Mafioso, the so-called John Gotti of Chicago. Lullo shows up at Firehouse 51 livid about the death of his son and threatens to kill Mills. This triggers Chicago P.D.’s involvement and Detective Halstead assures Mills that he will handle the situation.

Another call sends the squad to a burning furniture store that separates a husband from his wife. The desperation of the husband to find his wife forces Casey to recognize his own stubbornness with Dawson and he heads to Molly’s to apologize. When he arrives, however, he overhears Dawson in an intimate chat with Mills. She admits to doubting her relationship with Casey… and Mills takes her hand. Once Dawson and Mills see Casey gawking in the doorway, he turns back around. And he doesn’t look happy. Ouch…what will this mean for them both? Gear up for the fall finale. Here’s a sneak peak.

http://youtu.be/coCS1l73Qqs