In New York City, Anna Mitchell climbs into Wahid Davi's cab heading to LaGuardia. Apologizing to his fare, he floors it, careening the cab into the back of a truck. Both driver and passenger are immolated on contact. In an office, Milton Bobbit makes a call to transfer funds, then shreds a photo of Davi. Done with work, Milton returns to his cave-like apartment, which is more like a mushroom farm, to take his temperature, make a mushroom shake, and remove his prosthetic nose. His body rife with sores, Milton is clearly a very sick man.
Liz struggles to maintain her secret knowledge about Tom. After making breakfast, Tom gets down on one knee and asks Liz to renew their marriage vows. Liz accepts, but she's furious. Once Tom leaves for work, she rips up the house, looking for evidence to start her investigation out of a rented storage unit. She's in a bad way by the time Red arrives with news that he's been monitoring Tom since he entered her life. Not long ago Tom commissioned passports from one of Red's trusted forgers. Luckily, Red got his hands on the surveillance footage the Apple Man took of Liz's apartment. Clearly, the people Tom works for are very cautious; Red has spent years drawing them out. This is a unique opportunity! But Liz will need to take a case in order to keep her cool. The Undertaker is a broker of death, recruiting ordinary people to kill on his behalf - and then kill themselves. And in fact, Milton has already arranged the next kill. Dee Torres approaches Bennett Cochran at a gas station. After dumping gas all over the place, she lights both of them on fire. In short order, Liz is presenting the case to the FBI.
Liz, Meera and Ressler soon find a common thread among the killers: they were both terminally ill, mentally unstable and had families they were determined to support after their passing. The Undertaker, whom we now know as Milton Bobbit, has moved on to his next target, Danny Moss. Milton clearly knows all there is to know about Danny, including the right dollar figure to persuade him to kill. Meanwhile, Aram has uncovered The Undertaker's payment network through a bank in the Caymans, which leads the FBI to Danny Moss. Learning Danny is attending an election rally for Mitchell Travers, Liz and Ressler race to the scene to talk Danny down.
Tom comes home to find a party underway with his seldom-seen brother Craig in attendance. The vow renewal has been all set up. Liz thrusts champagne glasses into Craig and Tom's hands, forces a toast, then collects the wine glasses, sending Craig off to get Tom ready. Craig is convinced Liz is on to them, but Tom exudes confidence; he's got Liz wired. After the ceremony, Liz retreats to her storage unit to watch surveillance footage, trying to link Tom to various Blacklisters including Gina Zanetakos, who said she was Tom's lover. Having rigged their home with cameras, Liz spies on Tom removing a blue key from the base of their beloved lamp, Ike, which she gives to Dembe along with Craig's champagne glass. Red travels to El Salvador to persuade an old friend to do a rare touch DNA test on the glass to discover Craig's true identity, then calls Liz. After advising Liz to find out how The Undertaker knows his assassins are terminally ill, Red tells her to find Craig.
Liz waits for Craig outside his hotel room, then attacks, quickly taking him down and chaining him to the bathroom sink. She knows his real name is Christopher Maly, but she can't get anything else out of him, other than she has no idea who she's dealing with. Red knocks just as Liz gets called in to work. There she learns that all the assassins had policies at the same life insurance company. Liz begs out of the office visit, claiming she has a personal matter. Meera and Ressler discover Milton is the man they want to talk to, but oddly, he has disappeared from both work and home. Luckily, he has left behind files on the victims, including one on Dr. Frederick Osborne, presumably the next mark, whom Milton is presently abducting at gunpoint.
Red takes Christopher to a museum where he can see Dembe wheeling his mother around, a clear threat. Back at the hotel room, Christopher is ready to talk, but doesn't say much, other than he gets his instructions over the phone, no names. He mentions Tom has a brother in Chicago and there's a woman named Niki. Just then Tom calls Craig for a meeting, claiming he's accountable to Berlin. Knowing Tom is moments away, Liz and Red start preparing to get Craig out of the hotel. Refusing to say anything else about Berlin, Christopher hurls himself out of the window.
It turns out Milton was Osborne's patient zero for clinical trials on an experimental diabetes drug that resulted in his terminal condition. After figuring out that all The Undertaker's recent victims were involved in the trial, the FBI tracks Osborne, who's gone missing. Cornered in the cemetery of a church where he does volunteer work, Osborne is kept docile by virtue of the suicide bomb strapped to Milton's chest. Liz joins Meera and Ressler at the cemetery. With no negotiator, Ressler steps in and arrests Osborne for conspiracy for rigging the clinical trials, leaving Milton to blow himself up in peace. While Meera and Ressler pack up Milton's apartment, Liz returns to her storage unit, the blue key boring a hole in her mind - what does it unlock? After taking a few moments with Cooper's database, Red tells Liz that their focus should be whatever is going on in Berlin. Near hysteria, Liz claims she can't pretend anymore. Red advises her to stay the course; things have been set in motion with Christopher's death. So Liz returns home, where seduction is imminent.