After Firehouse 51 responds to a series of teen opioid overdoses, Intelligence gets involved to find out who has been selling the counterfeit OxyContin.
Sean Roman then randomly shows up at 51 and says his sister Sarah, who was friends with one of victims who overdosed and died, is missing.
Roman and Severide go talk to Boden's wife Donna, who works at the school Sarah goes to.
A friend of Sarah's tells Roman his sister had an older boyfriend who deals drugs.
At this point, Severide wants to loop in Intelligence, but Roman refuses, not wanting to tell Voight and the rest of the team until he has proof.
The pair then go to see a source and get confirmation about the boyfriend, but Roman still refuses to let Intelligence know what is going on.
Fearing for Roman's safety, Severide apprises Intelligence of the situation, unaware that no one even knew Roman was in Chicago.
Firehouse 51 later responds to a fire and finds Roman on the scene.
He says he was there to confront his sister's boyfriend who managed to escape out the back during the fire.
Elsewhere, a conflicted Brett finally decides to meet her birth mother.
She and Casey go to the address on the letter, but the man who answers the door claims Julie, her birth mother, doesn't live there.
Brett is heartbroken.
Shortly thereafter, Julie shows up at 51 and apologizes to Brett for how her husband mishandled the situation. Julie then reveals she is pregnant.