When the team gets called to the site of a meth lab, Boden institutes a station-wide mandatory drug test to make sure everyone's in the clear. This gives Severide some serious reason to worry, as he's been popping some heavy painkillers without a prescription. Severide goes to Shay with his issue, and she unsympathetically delivers the harsh news that there's really no work-around in this scenario.
Later, the team gets called to site of a gang shooting, which appears to still be in action. Using their trucks as shields, the team manages to create a protected area around two gunned down victims, one of which turns out to be Cruz's brother. Cruz is horrified to find that his brother is mixed up in this business, and later visits him at the hospital offering him a lecture-free ride home. But when Cruz shows up the next morning, his brother has already checked out and is nowhere to be found.
Boden notices a young boy hanging around the past few fire incidents, and decides to take him under his wing, hoping for some insight. Could Boden have a troublesome firebug on his hands? He invites him back to the station and has Herrmann do some intel, and soon finds out that the boy is being raised by his absent-minded grandmother. Herrmann notes that it's a definite possibility that the child is responsible for the fires, but there's no way to really be sure. When Boden asks to see the contents of the boy's backpack, looking for answers, the young boy gets spooked and runs off.
Always the chef, Mills is hard at work preparing Thanksgiving dinner for the team. His sister even comes by to help out, and she and Severide get engaged in some heavy cooking flirtation. Meanwhile, a representative comes to collect urine samples for the drug test, and Severide is visibly worried when his name is called. But he's saved by the bell when the gang gets called to the site of a 10-car pile up.
On the accident scene, everyone has their hands full in what appears to be a full-blown disaster. When Casey manages to free a car with a young couple stuck inside, he finds that the woman is pregnant and going into labor from the stress. He tries to call Shay and Dawson over but it's no use; the baby is coming and he has to deliver it on his own. With Shay and Dawson's instruction over the phone, Casey delivers the baby, but is horrified to find it not breathing. But using CPR, Casey manages to revive the child and deliver a happy ending!
Back at the station, Severide has run out of excuses for not handing over his urine sample. He regretfully goes into the restroom, but is saved just in time by Shay, who walks in, urine sample in hand. Despite the fact that she doesn't approve of his behavior, she can't watch him go down this way.
After the seemingly never-ending calls on Thanksgiving day, the team FINALLY sits down to dinner. Boden toasts to a clean bill of health for the entire team, as all the drug tests came back negative. Everyone gets down to eating and the mood is warm, loving, and carefree; this team is truly a family. Dawson congratulates Casey on delivering the baby, as it's truly an amazing accomplishment.
Later at home, Casey excitedly explains how he delivered and revived a baby to Hallie, amazed at how precious the gift of life is. He grabs Hallie's face in his hands, passionately telling her that he wants to have a baby with her, and he wants to do it soon. Hallie pulls away, and admits to Casey that she doesn't know if she'll ever want kids. She only wants them because Casey does, but she worries that that may not be enough. The question is, if kids are off the table, where does that leave Casey and Hallie?