The Chronological Viewing Order of Every Major ‘One Chicago’ Crossover

The interconnected television universe created by Dick Wolf weaves narrative arcs across ‘Chicago Fire’, ‘Chicago P.D.’, and ‘Chicago Med’. Viewing these collaborative multi-part storylines in chronological order ensures a seamless experience as characters respond to citywide crises together.

While early events connected only two series prior to the premiere of ‘Chicago Med’, later events expanded into massive three-part multi-series emergencies. Following the broadcast order of these interconnected storylines allows viewers to appreciate the complex narrative continuity of the franchise.

The Firehouse 51 Bombing (2014)

The two-part crossover begins in ‘Chicago Fire’ with the episode ‘A Dark Day’, where a devastating explosion strikes Chicago Medical Center during a charity road race. First responders from Firehouse 51 quickly initiate rescue efforts in the rubble while evacuating injured civilians and attending to wounded colleagues. The storyline concludes in ‘Chicago P.D.’ with the episode ‘8:30 PM’, shifting focus to Sergeant Hank Voight and the Intelligence Unit as they search for the bombers. Detectives and firefighters work in tandem across the city to locate the primary suspect and defuse a secondary explosive device before further casualties occur.

The Arson / Vegas Crossover (2015)

This investigation launches in the ‘Chicago Fire’ episode ‘Three Bells’, following the discovery of new evidence linking the fatal fire that killed paramedic Leslie Shay to a serial arsonist. Lieutenant Kelly Severide partners with the Intelligence Unit to track the arsonist’s movements after uncovering a series of suspicious fires dating back several years. The narrative resolves in the ‘Chicago P.D.’ episode ‘A Little Devil Complex’, where detectives identify the elusive suspect operating under multiple aliases. Intelligence pursues the dangerous pyromaniac through an intense standoff to secure justice for the fallen paramedic.

The Nesbitt Case (2015)

The two-part season finale begins in the ‘Chicago Fire’ episode ‘Spartacus’, as Lieutenant Matthew Casey uncovers illegal operations linked to strip club owner Scott Nesbitt. Sergeant Voight recruits Casey to operate undercover to help the Intelligence Unit build an airtight federal human trafficking case. The plot concludes in the ‘Chicago P.D.’ season finale ‘Born Into Bad News’, where Casey’s undercover role places him in direct danger with armed criminals. Intelligence executes a tactical raid to take down Nesbitt’s trafficking organization and rescue Casey from captivity.

The Poisoned Victims Crossover (2016)

The franchise’s first official three-way storyline opens in the ‘Chicago Fire’ episode ‘The Beating Heart’, where firefighter Christopher Herrmann is rushed to the hospital following a violent stabbing. The narrative continues in the ‘Chicago Med’ episode ‘Malignant’, where attending physicians discover that several dying cancer patients received lethal overdoses of chemotherapy despite being completely cancer-free. The case culminates in the ‘Chicago P.D.’ episode ‘Now I’m God’, focusing on the Intelligence Unit’s criminal probe into the rogue oncologist responsible for the deadly treatments. Sergeant Voight leads the investigation into the doctor’s malpractice, revealing personal ties that impact his team as they secure formal charges.

The Apartment Building Fire (2018)

This three-part event begins in the ‘Chicago Fire’ episode ‘Going to War’, as firefighters combat a massive inferno consuming a 25-story residential high-rise. The crisis moves to the ‘Chicago Med’ episode ‘When to Let Go’, where emergency personnel manage a sudden influx of burn victims, including Detective Jay Halstead’s critically injured father. The storyline concludes in the ‘Chicago P.D.’ episode ‘Endings’, as the Intelligence Unit establishes that the fire was an intentional act of arson orchestrated by a cartel operative. Detectives track the perpetrator through the streets of Chicago to hold the cartel accountable for the devastating loss of life.

Infection (2019)

The three-show crossover initiates in the ‘Chicago Fire’ episode ‘Infection: Part I’, when an aggressive flesh-eating biological pathogen strikes civilians near a university tailgate. The medical crisis escalates in the ‘Chicago Med’ episode ‘Infection: Part II’, where doctors and epidemiologists scramble to treat quarantined patients while identifying the engineered bacterium. The narrative concludes in the ‘Chicago P.D.’ episode ‘Infection: Part III’, with the Intelligence Unit tracking a rogue scientist who weaponized the bacteria to target the city. All three emergency divisions coordinate across Chicago to locate the perpetrator and prevent a catastrophic biological dispersal downtown.

The Toxic Chemical Crossover (2020)

The two-part crossover starts in the ‘Chicago Fire’ episode ‘Off the Grid’, as paramedics treat numerous young victims overdosing on counterfeit opioid pills laced with toxic chemicals. Former police officer Sean Roman returns to Chicago to investigate his missing sister, collaborating with Firehouse 51 to trace the fatal drug supply. The arc wraps up in the ‘Chicago P.D.’ episode ‘Burden of Truth’, where Voight’s unit targets the dealer responsible as the search for Roman’s sister turns into a homicide investigation. Medical personnel from ‘Chicago Med’ also assist by providing treatment to victims and analyzing the lethal chemical compounds in hospital facilities.

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