The FBI's next target protects the guilty by preying on the DNA of the innocent. Ryan O'Nan guest stars.
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.