Red and the FBI try to stop a dangerous messenger (Robert Knepper) whose appearance is unknown; Liz is thrust into a kidnapping plot.

Red informs the team that "The Alchemist" - a man who relies upon science to transform a person’s DNA - has been contracted to protect a well-known mob informant and his wife. As the team goes undercover to catch him, Liz finds herself on the hunt for an unlikely couple. Meanwhile Liz and Tom find themselves at another bump in their relationship and Ressler debates whether or not he should give his ex-girlfriend his blessing.