Elizabeth reluctantly seeks Red's help finding the next person on the blacklist, brilliant scientist Frederick Barnes (guest star Robert Sean Leonard).
Barnes succeeds in producing a potential antidote, but Liz kills him to prevent him from injecting it into his son.
[5] He commended Robert Sean Leonard's portrayal of Frederick Barnes, but felt his character "wasn’t all that important to the overall storyline of the show".
[6] He appreciated that the show made characters like Raymond Reddington "have a multilayered nature that makes them more sympathetic".
I mean at this point, the most we know about the past of Elizabeth is that her father abandoned her as a child, she and her husband went on vacation at the same time and place as a person who died and that they have named their IKEA lamp Ike".