SO many of the lines in this show...especially from Irina...that are just wonderful! But I think my top choice has to be this:
IRINA: I know what you did for me. Proving Sydney's father betrayed her in Madagascar. I would have been executed for that. Thank you.
VAUGHN: I didn't do it for you.
(Irina gets up and walks to the glass. Vaughn looks down, avoiding eye contact.)
IRINA: While that might be true, I owe you my life.