|Ryan Eggold as Tom Keen. Photo Credit: Will Hart/NBC|
Red (James Spader) informs the team that "The Alchemist" (guest star Ryan O'Nan) - 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 (Megan Boone) finds herself on the hunt for an unlikely couple.
Meanwhile, Liz and Tom (Ryan Eggold) find themselves at another bump in their relationship and Ressler (Diego Klattenhoff) debates whether or not he should give his ex-girlfriend his blessing.
Check out a sneak peek video below:
Parminder Nagra and Harry Lennix also star.