Knowing that Tom isn’t who he seems, Liz is suspicious when he asks to renew their wedding vows. When she presses for answers, Red admits to tracking Tom’s movements ever since he entered her life. After turning over his surveillance files for her to examine, he alerts Liz to a new Blacklist target known as the Undertaker, who can get strangers to murder on his behalf before killing themselves. In the wake of two recent killings, the FBI discovers that both assassins were terminally ill – and because their family’s financial problems were mysteriously taken care of after the murders, Cooper suspects the Undertaker’s at work. Meanwhile, as Liz sets out to use their vow renewal party to gather more evidence about him, Tom’s “brother,” an intelligence team operative named Christopher Maly, warns Tom that Liz is on to him.
After uncovering the money trail used to pay the suicide killers, Aram learns that the Undertaker’s next assassin is a dying man named Danny Moss. Stopping him as he’s about to strike, Liz and Ressler take Moss into custody. After ambushing Maly in his hotel room, Liz leaves him with Red and Dembe, who make it clear that his elderly mother will pay the price for his silence. Along with Ressler, Liz meets with a life insurance company that recently cancelled policies for all three killers – the same place where the Undertaker, aka Milton Bobbit, works. Though Bobbit runs when he sees he’s been discovered, Liz and Ressler search his home and find a file on his next target, Dr. Frederick Osborne. Meanwhile, when Liz joins Red and Dembe at the hotel to question him about Tom, Maly jumps to his death to avoid talking.
After linking the last three murder victims to a diabetes drug trial conducted by Osborne, Ressler learns that Bobbit was the experiment’s “Patient Zero.” Outfitted with a suicide vest, Bobbit kidnaps Osborne and takes him to a cemetery where he works as a volunteer. Explaining how being disfigured during the trial prompted his crusade to avenge those patients who died needlessly, Bobbit prepares to kill Osborne and himself just as the FBI arrives. So when Ressler moves to arrest Osborne for murder, Bobbit sees his work is done and commits suicide. Finally, though Liz says that she’s had enough, Red convinces her to continuing playing along in order to get to the bottom of Tom’s plan.