Andy and Officer Marlo Cruz, Swarek's new girlfriend, butt heads on their first patrol together. Their different ways of handling the job are put to the test when they confront an emotionally disturbed woman who is losing control - and explode when one of them is forced to make a crucial life-saving decision to pull the trigger. Meanwhile, the rest of 15 Division is hunting down an armed burglar with a novel MO after a string of ATM robberies, and Dov is forced to work with new rookie Chloe Price after their indiscreet first encounter.

A chaotic drug arrest by Andy and Marlo triggers an all-out crisis when it's discovered that the drugs are contaminated with deadly bacteria. Swarek leads the squad in the scramble to get the tainted drugs off the streets before an outbreak sweeps the city. Meanwhile, Andy and Marlo are plunged into an intimate decontamination process, forcing Marlo to expose a shocking secret while under quarantine. And Dov and Chloe see their budding romance threatened when Dov suspects Chloe is hiding secrets.