As the Justice Department prepares Luis Pena to testify against cartel boss Hector Lorca, Red tells Liz that the drug lord reached out to him for help and that the government’s case is about to fall apart. As the only witness to the kidnapping of his son, Border Patrol agent Bobby Pena, Luis arrives in court to testify that Lorca – the suspect in the deaths of more than 100 other witnesses against the cartel – ordered the crime. As Luis is about to identify Lorca, the trial is halted by a juror’s suspicious heart attack. When Luis says he’s worried for his wife’s safety, Liz leaves him in the custody of the U.S. Marshals as she goes to find her. But as Ressler learns that the heart attack was chemically induced to disrupt the proceedings, Luis is kidnapped by cartel henchmen posing as the Marshals assigned to protect him. Meanwhile, in the wake of the ballistics tests on the gun she found at home, Liz steals the case file from the Bureau’s evidence room.
While brokering the sale of Stinger missiles in Haiti, Red tells Liz that Luis’ disappearance is the work of the Stewmaker, an assassin who chemically dissolves his victims to destroy any evidence of their murders. To find him and close hundreds of unsolved murder cases, he suggests pressuring Lorca. Though they offer him a deal, Lorca says he’ll take his chances fighting the charges against him. However, as he’s being transferred to a secure Homeland Security prison, Lorca’s henchmen unleash a rocket attack to free him and kidnap Liz. When Red offers to negotiate Liz’s release, Ressler insists on going along and is forced to pose as a corrupt cop to keep from getting killed. To get Red to aid in his escape, Lorca provides a tip that helps Meera identify the Stewmaker as Maryland dentist Stanley Kornish.
As Meera and Ressler question Kornish’s wife, Red looks for Liz by using GPS to track Kornish’s emotional support dog, Blaze. With Kornish preparing to dissolve her, Liz works to get inside his head as she struggles to remain conscious and escape. But when Red catches up with them, she watches in horror as he dissolves the Stewmaker in acid. Though Ressler is upset that Lorca got away, Red assures him that he’s on a private jet from which there is no escape. Finally, as Red recovers a photo from the assassin’s collection of victims’ pictures, Liz finds more evidence connecting Tom to a murder committed with the hidden gun.