While out on a bank run for his off-duty security job at the dispensary, Halstead and his co-workers find themselves under attack by a violent robbery crew which quickly becomes a full-scale shootout. Voight and Lindsay question the owner of the dispensary who mentions her business has received threats from local gangs upset she's cutting into their revenue. Meanwhile Roman, Burgess, Antonio, Halstead, Ruzek and Atwater follow-up on a lead and track down a potential suspect.