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.

The grisly discovery of human bones in a ravine re-opens a 15-year-old missing persons case, and Swarek teams up with his old training officer, Charlie Walsh, in an effort to close the case. But an up-close-and-personal look at Charlie's life makes Swarek think twice about whether he wants to continue in his mentor's footsteps. And a weird night gets even stranger when Chloe and Dov can't agree with how to deal with a witch and her disgruntled client.