Season 4 Episode 4
"Your Day Is Coming"
Severide suspects an insider at Arson is hiding evidence that could exonerate the squad; 51 rallies around Dawson and her unborn baby.
After collapsing at the end of the last episode, an unresponsive Dawson (Monica Raymund) is wheeled on a gurney into Chicago Med. Although the doctors are able to stop Dawson's internal bleeding and save her life, she loses her baby.
Severide (Taylor Kinney) investigates the missing arson files (needed in the conspiracy case against real estate developer Roger Maddox) and concludes that their disappearance must have been an inside job. His suspicions are confirmed when Duff, Dawson's Arson supervisor, leaves the files at Firehouse 51 - and then tries to kill himself. Guilt-ridden, Duff had accepted a bribe from Maddox's people to hand off the files from inside Arson. Duff survives, and the evidence he turned over effectively closes the investigation surrounding 51's actions in the crack house fire.
Molly's is shut down (due to two Portland interlopers) but is saved from closure when it is declared a historical landmark. Herrmann (David Eigenberg) sends a video message to Dawson at the hospital, where he implores her to hang in there because "your day is coming."